diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9fb11b81..d5e12276 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,8 +5,6 @@ on:
     branches:
       - main
   pull_request:
-    branches:
-      - main
 
 permissions:
   contents: read
@@ -36,9 +34,21 @@ jobs:
       - name: Check public feature builds
         run: npm run check:features
 
+      - name: Verify packed consumers
+        run: npm run check:consumer
+
+      - name: Run negative compiler consumers
+        run: npm run test:negative
+
       - name: Run tests
         run: npm test
 
+      - name: Install Chromium
+        run: npx playwright install --with-deps chromium
+
+      - name: Run browser tests
+        run: npm run test:browser
+
       - name: Build documentation
         run: npm run build:docs
 
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 95c14944..e547814b 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -2,12 +2,10 @@ name: Release
 
 on:
   pull_request:
-    branches:
-      - main
   workflow_dispatch:
     inputs:
       dry_run:
-        description: Run npm publish without publishing the package
+        description: Validate and dry-run without publishing
         required: true
         default: true
         type: boolean
@@ -16,11 +14,8 @@ permissions:
   contents: read
 
 jobs:
-  publish:
+  validate:
     runs-on: ubuntu-latest
-    permissions:
-      contents: read
-      id-token: write
 
     steps:
       - name: Checkout repository
@@ -30,7 +25,6 @@ jobs:
         uses: actions/setup-node@v7
         with:
           node-version: "26"
-          registry-url: https://registry.npmjs.org
           package-manager-cache: false
 
       - name: Setup npm
@@ -48,39 +42,124 @@ jobs:
       - name: Check public feature builds
         run: npm run check:features
 
+      - name: Verify packed consumers
+        run: npm run check:consumer
+
+      - name: Run negative compiler consumers
+        run: npm run test:negative
+
       - name: Run tests
         run: npm test
 
+      - name: Install Chromium
+        run: npx playwright install --with-deps chromium
+
+      - name: Run browser tests
+        run: npm run test:browser
+
       - name: Build documentation
         run: npm run build:docs
 
-      - name: get-npm-version
-        id: package-version
-        uses: martinbeentjes/npm-get-version-action@v1.3.1
+      - name: Validate explicit alpha version and unpublished state
+        run: npm run check:release
+
+      - name: Package release artifact
+        id: package
+        run: |
+          mkdir -p .release
+          npm pack --json --pack-destination .release > .release/metadata.json
+          artifact="$(node -e 'process.stdout.write(JSON.parse(require("node:fs").readFileSync(".release/metadata.json", "utf8"))[0].filename)')"
+          echo "artifact=.release/$artifact" >> "$GITHUB_OUTPUT"
+
+      - name: Verify packed consumers and tarball contents
+        run: npm run check:consumer -- "${{ steps.package.outputs.artifact }}"
 
-      - name: Get short commit hash
-        id: vars
-        run: echo "COMMIT_HASH=$(git rev-parse --short HEAD)" >> $GITHUB_ENV
+      - name: Dry-run publish the validated artifact
+        run: npm publish "${{ steps.package.outputs.artifact }}" --access public --tag alpha --dry-run
 
-      - name: Update package version to -<commit-hash>
-        env:
-          PACKAGE_VERSION: ${{ steps.package-version.outputs.current-version }}-alpha-${{ env.COMMIT_HASH }}
+      - name: Reject real publication from non-main branches
+        if: github.event_name == 'workflow_dispatch' && !inputs.dry_run && github.ref != 'refs/heads/main'
         run: |
-          node <<'NODE'
-          const fs = require("node:fs");
-          const packageJsonPath = "package.json";
-          const packageJson = JSON.parse(fs.readFileSync(packageJsonPath, "utf8"));
-          packageJson.version = process.env.PACKAGE_VERSION;
-          fs.writeFileSync(packageJsonPath, `${JSON.stringify(packageJson, null, 2)}\n`);
+          echo "Real alpha publication is permitted only from main."
+          exit 1
+
+      - name: Upload validated release artifact
+        if: github.event_name == 'workflow_dispatch' && github.ref == 'refs/heads/main' && !inputs.dry_run
+        uses: actions/upload-artifact@v4
+        with:
+          name: alpha-release-artifact
+          path: ${{ steps.package.outputs.artifact }}
+          if-no-files-found: error
+          retention-days: 1
+
+  publish:
+    needs: validate
+    if: github.event_name == 'workflow_dispatch' && github.ref == 'refs/heads/main' && !inputs.dry_run
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      id-token: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v7
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v7
+        with:
+          node-version: "26"
+          registry-url: https://registry.npmjs.org
+          package-manager-cache: false
+
+      - name: Setup npm
+        run: npm install --global npm@11.5.1
+
+      - name: Download validated release artifact
+        uses: actions/download-artifact@v4
+        with:
+          name: alpha-release-artifact
+          path: .release
+
+      - name: Verify downloaded artifact metadata
+        run: |
+          artifact=".release/rescript-webapi-$(node -p 'require("./package.json").version').tgz"
+          test -f "$artifact"
+          node --input-type=module <<'NODE'
+          import { execFileSync } from "node:child_process";
+          import { readFileSync } from "node:fs";
+          const { name, version, publishConfig } = JSON.parse(readFileSync("package.json", "utf8"));
+          const artifact = `.release/rescript-webapi-${version}.tgz`;
+          const packed = JSON.parse(execFileSync("tar", ["-xOf", artifact, "package/package.json"], { encoding: "utf8" }));
+          if (packed.name !== name || packed.version !== version || !/^1\.0\.0-alpha\.[1-9]\d*$/.test(version)) {
+            throw new Error("Downloaded artifact does not match the numbered alpha package metadata.");
+          }
+          if (publishConfig.access !== "public" || publishConfig.provenance !== true) {
+            throw new Error("Downloaded artifact is missing public/provenance publishing metadata.");
+          }
+          const publishLifecycleScripts = ["prepare", "prepack", "prepublishOnly", "publish", "postpublish"];
+          if (publishLifecycleScripts.some((script) => packed.scripts?.[script] !== undefined)) {
+            throw new Error("Downloaded artifact contains a publish lifecycle script.");
+          }
+          console.log(`Verified ${name}@${version} artifact before publishing with the alpha tag.`);
           NODE
 
-      - name: Package npm package
-        run: npm pack
+      - name: Verify publication guard
+        run: npm run check:release -- --publish
 
-      - name: Dry-run npm publish
-        if: github.event_name == 'pull_request' || inputs.dry_run
-        run: npm publish ./rescript-webapi-*.tgz --access public --tag alpha --dry-run
+      - name: Publish alpha artifact
+        run: npm publish ".release/rescript-webapi-$(node -p 'require("./package.json").version').tgz" --access public --tag alpha --provenance
 
-      - name: Publish npm package
-        if: github.event_name == 'workflow_dispatch' && github.ref == 'refs/heads/main' && !inputs.dry_run
-        run: npm publish ./rescript-webapi-*.tgz --access public --tag alpha
+      - name: Verify alpha dist-tag
+        run: |
+          node <<'NODE'
+          const { execFileSync } = require("node:child_process");
+          const { name, version } = require("./package.json");
+          const tags = JSON.parse(execFileSync("npm", ["view", name, "dist-tags", "--json"], { encoding: "utf8" }));
+          if (tags.alpha !== version) {
+            throw new Error(`Expected alpha dist-tag ${version}, received ${tags.alpha ?? "missing"}.`);
+          }
+          if (tags.latest === version) {
+            throw new Error(`Alpha publication unexpectedly advanced latest to ${version}.`);
+          }
+          console.log(`Verified ${name}@${version} is tagged alpha and not latest.`);
+          NODE
diff --git a/.gitignore b/.gitignore
index 24b4284b..abe3638e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,8 +3,12 @@
 .bsb.lock
 .astro
 dist/
+.release/
 tmp/
 docs/public/llm.txt
+.playwright/
+/test-results/
+/playwright-report/
 .npm-cache/
 *.tgz
 *~
diff --git a/docs/content/docs/contributing/testing.mdx b/docs/content/docs/contributing/testing.mdx
index a5e8eaf6..18c63947 100644
--- a/docs/content/docs/contributing/testing.mdx
+++ b/docs/content/docs/contributing/testing.mdx
@@ -4,24 +4,27 @@ description: Learn more about testing the bindings for @rescript/webapi.
 slug: "06-testing"
 ---
 
-import { Aside, FileTree } from "@astrojs/starlight/components";
+import { FileTree } from "@astrojs/starlight/components";
 
 Adding some unit tests is a great way to ensure that the bindings work as expected.
 It illustrates how the bindings are supposed to be used and can help to catch regressions.
 
 ## Testing the bindings
 
-Create a new help in the `test` folder with the same name as the module you want to test, followed by `_test.res`.
+Add a ReScript fixture under `tests/`, following the source module's directory structure. Register
+each fixture in exactly one category in `tests/fixtures.json`: `compileOnly`,
+`documentationExamples`, `nodeRuntime`, or `browserRuntime`. `npm test` fails if a fixture is missing
+from the manifest or appears in multiple categories, compiles all fixtures, and executes only the
+Node runtime modules. Compile-only fixtures and documentation examples are never executed.
 
 <FileTree>
 
 - src
-  - DOMAPI.res
-  - DOMAPI
-    - HTMLCanvasElement.res
+  - fetch
+    - Headers.res
 - tests
-  - DOMAPI
-    - HTMLCanvasElement_test.res
+  - FetchAPI
+    - Headers\_\_test.res
 
 </FileTree>
 
@@ -33,12 +36,35 @@ git add tests
 npm test
 ```
 
-If any of the existing tests have different ouput JavaScript, you will see a diff in the output and the test will fail.
+Run the focused checks that match your fixture:
 
-<Aside>
-  Depending on your use-case, it might be okay to have slightly different output JavaScript. The
-  maintainers will help you to decide if the change is acceptable.
-</Aside>
+```shell
+npm test                 # compile fixtures and execute Node-compatible runtime tests
+npm run test:browser     # execute native-browser regressions in Chromium
+npm run test:negative    # verify expected compiler failures and diagnostics
+```
+
+Use the browser suite for APIs that require a real browser. Node's built-in Fetch support is useful
+for Node runtime coverage, but is not a substitute for Chromium validation; DOM emulators are not
+browser evidence either. Keep examples that need special setup, such as a GET request with a body,
+compile-only unless they are deliberately configured as a runtime fixture.
+Browser fixtures with asynchronous behavior must await all assertions and callback completion before
+the ReScript module finishes evaluating; the browser runner awaits module evaluation and treats
+rejections and uncaught page errors as failures.
+
+Put expected-failure consumer sources under `scripts/fixtures/negative/`, outside the recursively
+compiled `tests/` tree. Register each in `scripts/negative-fixtures.json` with its feature set and a
+distinctive compiler diagnostic substring. The negative command must observe both compilation failure
+and that expected diagnostic; an unrelated compiler failure does not pass the check.
+
+## Installed package consumers
+
+Run `npm run check:consumer` to pack the current package, install that artifact with the supported
+ReScript compiler in a fresh temporary project, and compile representative feature consumers.
+This verifies the installed tarball rather than copied source files or local compiler links.
+The development compiler and the exact version exercised by this check are ReScript
+`13.0.0-alpha.5`. The peer range `>=13.0.0-alpha.5 <13.0.0` admits later `13.0.0` prereleases;
+it does not claim support for earlier compilers or stable `13.0.0`.
 
 ## Why add tests?
 
diff --git a/docs/llm.js b/docs/llm.js
index 4e957660..ff2c622a 100644
--- a/docs/llm.js
+++ b/docs/llm.js
@@ -145,11 +145,9 @@ files.sort();
 const pages = await Promise.all(files.map(processFile));
 const packageJson = await fs.readFile(path.join(import.meta.dirname, "../package.json"), "utf-8");
 const version = JSON.parse(packageJson).version;
-const sha = await execAsync("git rev-parse --short HEAD").then(({ stdout }) => stdout.trim());
-const fullVersion = `${version}-alpha-${sha}`;
-const header = `Experimental ReScript WebAPI Documentation ${fullVersion}
+const header = `Experimental ReScript WebAPI Documentation ${version}
 
-This is the API documentation for the experimental WebAPI module version ${fullVersion}.
+This is the API documentation for the experimental WebAPI module version ${version}.
 More information can be found on https://rescript-lang.github.io/experimental-rescript-webapi/
 
 `;
diff --git a/package-lock.json b/package-lock.json
index d06e3beb..d5fdbc4e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,25 +1,26 @@
 {
   "name": "@rescript/webapi",
-  "version": "0.1.0",
+  "version": "1.0.0-alpha.1",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "@rescript/webapi",
-      "version": "0.1.0",
+      "version": "1.0.0-alpha.1",
       "license": "MIT",
       "devDependencies": {
         "@astrojs/starlight": "0.42.8",
+        "@playwright/test": "^1.64.1",
         "astro": "^7.2.9",
         "micromark": "^4.0.1",
         "oxfmt": "^0.75.0",
         "prettier": "^3.8.3",
         "prettier-plugin-astro": "^1.0.0",
-        "rescript": "^13.0.0-alpha.4",
+        "rescript": "13.0.0-alpha.5",
         "sharp": "^0.35.3"
       },
       "peerDependencies": {
-        "rescript": ">=13"
+        "rescript": ">=13.0.0-alpha.5 <13.0.0"
       }
     },
     "node_modules/@astrojs/compiler-binding": {
@@ -1809,6 +1810,22 @@
         "win32"
       ]
     },
+    "node_modules/@playwright/test": {
+      "version": "1.64.1",
+      "resolved": "https://registry.npmjs.org/@playwright/test/-/test-1.64.1.tgz",
+      "integrity": "sha512-IaYGml/nSOiZWROfPtuIL7neuu9qDOZ3TNvNljUIrhDMxiGTgPjzj/g9p9RxpS2tSepPDRY+UwAaEeiKtUvIAg==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "dependencies": {
+        "playwright": "1.64.1"
+      },
+      "bin": {
+        "playwright": "cli.js"
+      },
+      "engines": {
+        "node": ">=20"
+      }
+    },
     "node_modules/@prettier/parse-srcset": {
       "version": "3.1.0",
       "resolved": "https://registry.npmjs.org/@prettier/parse-srcset/-/parse-srcset-3.1.0.tgz",
@@ -4115,10 +4132,11 @@
       }
     },
     "node_modules/mdast-util-to-hast": {
-      "version": "13.2.0",
-      "resolved": "https://registry.npmjs.org/mdast-util-to-hast/-/mdast-util-to-hast-13.2.0.tgz",
-      "integrity": "sha512-QGYKEuUsYT9ykKBCMOEDLsU5JRObWQusAolFMeko/tYPufNkRffBAQjIE+99jbA87xv6FgmjLtwjh9wBWajwAA==",
+      "version": "13.2.1",
+      "resolved": "https://registry.npmjs.org/mdast-util-to-hast/-/mdast-util-to-hast-13.2.1.tgz",
+      "integrity": "sha512-cctsq2wp5vTsLIcaymblUriiTcZd0CwWtCbLvrOzYCDZoWyMNV8sZ7krj09FSnsiJi3WVsHLM4k6Dq/yaPyCXA==",
       "dev": true,
+      "license": "MIT",
       "dependencies": {
         "@types/hast": "^3.0.0",
         "@types/mdast": "^4.0.0",
@@ -4980,6 +4998,35 @@
         "url": "https://github.com/sponsors/jonschlinkert"
       }
     },
+    "node_modules/playwright": {
+      "version": "1.64.1",
+      "resolved": "https://registry.npmjs.org/playwright/-/playwright-1.64.1.tgz",
+      "integrity": "sha512-HCrVhHr5QQuwYoswEUGTb7gGp522yflbv/ST8nF4sFWGuLjQCt17Q/EubpGGSNKYn1tsTCPZxqHhHCfVURu7UA==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "dependencies": {
+        "playwright-core": "1.64.1"
+      },
+      "bin": {
+        "playwright": "cli.js"
+      },
+      "engines": {
+        "node": ">=20"
+      }
+    },
+    "node_modules/playwright-core": {
+      "version": "1.64.1",
+      "resolved": "https://registry.npmjs.org/playwright-core/-/playwright-core-1.64.1.tgz",
+      "integrity": "sha512-BC4s8y6SEVA6Q1rSxZTto8hI1KUI3xXlHGZgvGqP4IqPdI/a6FX9H29IDNz7vKo9l21b6LfYosScPL6M3xxyDQ==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "bin": {
+        "playwright-core": "cli.js"
+      },
+      "engines": {
+        "node": ">=20"
+      }
+    },
     "node_modules/postcss": {
       "version": "8.5.31",
       "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.31.tgz",
@@ -5036,9 +5083,9 @@
       }
     },
     "node_modules/postcss-selector-parser": {
-      "version": "6.1.4",
-      "resolved": "https://registry.npmjs.org/postcss-selector-parser/-/postcss-selector-parser-6.1.4.tgz",
-      "integrity": "sha512-bIoJLOmjCO1S9XdY/DcnR5hJxvrDir1PbGChrzXG3vw0/FOliy/fA3dmdhQ441kah4gKv+TwckGzex6wNS5cnQ==",
+      "version": "6.1.5",
+      "resolved": "https://registry.npmjs.org/postcss-selector-parser/-/postcss-selector-parser-6.1.5.tgz",
+      "integrity": "sha512-TEHFzb5KRDKaOgJ4TYE+0jyJtFbjLvkdVOu0fZ2b6MTWzoqZd4Le+61aEppWkvTlYePgOX4ATL1wsAIPMLTw6Q==",
       "dev": true,
       "license": "MIT",
       "dependencies": {
@@ -6991,6 +7038,15 @@
       "dev": true,
       "optional": true
     },
+    "@playwright/test": {
+      "version": "1.64.1",
+      "resolved": "https://registry.npmjs.org/@playwright/test/-/test-1.64.1.tgz",
+      "integrity": "sha512-IaYGml/nSOiZWROfPtuIL7neuu9qDOZ3TNvNljUIrhDMxiGTgPjzj/g9p9RxpS2tSepPDRY+UwAaEeiKtUvIAg==",
+      "dev": true,
+      "requires": {
+        "playwright": "1.64.1"
+      }
+    },
     "@prettier/parse-srcset": {
       "version": "3.1.0",
       "resolved": "https://registry.npmjs.org/@prettier/parse-srcset/-/parse-srcset-3.1.0.tgz",
@@ -8075,7 +8131,7 @@
         "comma-separated-tokens": "^2.0.0",
         "hast-util-whitespace": "^3.0.0",
         "html-void-elements": "^3.0.0",
-        "mdast-util-to-hast": "^13.0.0",
+        "mdast-util-to-hast": "^13.2.1",
         "property-information": "^7.0.0",
         "space-separated-tokens": "^2.0.0",
         "stringify-entities": "^4.0.0",
@@ -8412,9 +8468,9 @@
       }
     },
     "mdast-util-to-hast": {
-      "version": "13.2.0",
-      "resolved": "https://registry.npmjs.org/mdast-util-to-hast/-/mdast-util-to-hast-13.2.0.tgz",
-      "integrity": "sha512-QGYKEuUsYT9ykKBCMOEDLsU5JRObWQusAolFMeko/tYPufNkRffBAQjIE+99jbA87xv6FgmjLtwjh9wBWajwAA==",
+      "version": "13.2.1",
+      "resolved": "https://registry.npmjs.org/mdast-util-to-hast/-/mdast-util-to-hast-13.2.1.tgz",
+      "integrity": "sha512-cctsq2wp5vTsLIcaymblUriiTcZd0CwWtCbLvrOzYCDZoWyMNV8sZ7krj09FSnsiJi3WVsHLM4k6Dq/yaPyCXA==",
       "dev": true,
       "requires": {
         "@types/hast": "^3.0.0",
@@ -8922,6 +8978,21 @@
       "integrity": "sha512-qcJu88Q2IWqJsDD529JKMdwGm/dvInW4HvQnRwiH9JtihJvzGOscDtHE3x1pBKeUOTysQ8kVmLnJ2kJu7yhcGA==",
       "dev": true
     },
+    "playwright": {
+      "version": "1.64.1",
+      "resolved": "https://registry.npmjs.org/playwright/-/playwright-1.64.1.tgz",
+      "integrity": "sha512-HCrVhHr5QQuwYoswEUGTb7gGp522yflbv/ST8nF4sFWGuLjQCt17Q/EubpGGSNKYn1tsTCPZxqHhHCfVURu7UA==",
+      "dev": true,
+      "requires": {
+        "playwright-core": "1.64.1"
+      }
+    },
+    "playwright-core": {
+      "version": "1.64.1",
+      "resolved": "https://registry.npmjs.org/playwright-core/-/playwright-core-1.64.1.tgz",
+      "integrity": "sha512-BC4s8y6SEVA6Q1rSxZTto8hI1KUI3xXlHGZgvGqP4IqPdI/a6FX9H29IDNz7vKo9l21b6LfYosScPL6M3xxyDQ==",
+      "dev": true
+    },
     "postcss": {
       "version": "8.5.31",
       "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.31.tgz",
@@ -8939,13 +9010,13 @@
       "integrity": "sha512-HQbt28KulC5AJzG+cZtj9kvKB93CFCdLvog1WFLf1D+xmMvPGlBstkpTEZfK5+AN9hfJocyBFCNiqyS48bpgzQ==",
       "dev": true,
       "requires": {
-        "postcss-selector-parser": "^6.1.1"
+        "postcss-selector-parser": "^6.1.5"
       }
     },
     "postcss-selector-parser": {
-      "version": "6.1.4",
-      "resolved": "https://registry.npmjs.org/postcss-selector-parser/-/postcss-selector-parser-6.1.4.tgz",
-      "integrity": "sha512-bIoJLOmjCO1S9XdY/DcnR5hJxvrDir1PbGChrzXG3vw0/FOliy/fA3dmdhQ441kah4gKv+TwckGzex6wNS5cnQ==",
+      "version": "6.1.5",
+      "resolved": "https://registry.npmjs.org/postcss-selector-parser/-/postcss-selector-parser-6.1.5.tgz",
+      "integrity": "sha512-TEHFzb5KRDKaOgJ4TYE+0jyJtFbjLvkdVOu0fZ2b6MTWzoqZd4Le+61aEppWkvTlYePgOX4ATL1wsAIPMLTw6Q==",
       "dev": true,
       "requires": {
         "cssesc": "^3.0.0",
diff --git a/package.json b/package.json
index 76f4fa8d..e900c0fa 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@rescript/webapi",
-  "version": "0.1.0",
+  "version": "1.0.0-alpha.1",
   "description": "Experimental successor to [rescript-webapi](https://github.com/TheSpyder/rescript-webapi)",
   "keywords": [
     "dom",
@@ -36,26 +36,35 @@
     "provenance": true
   },
   "scripts": {
-    "test": "node tests/index.js",
+    "test": "rescript clean && node tests/index.js",
+    "test:browser": "rescript clean && npm run build && playwright test",
+    "test:negative": "node scripts/check-consumer.mjs --negative-only",
     "build": "rescript",
     "check:features": "node --test scripts/check-features.test.mjs && node scripts/check-features.mjs",
-    "format": "rescript format && oxfmt ./tests/index.js ./scripts/check-features.mjs ./scripts/check-features.test.mjs ./package.json ./docs && prettier --write ./docs/pages",
-    "format:check": "rescript format --check && oxfmt ./tests/index.js ./scripts/check-features.mjs ./scripts/check-features.test.mjs ./package.json ./docs --check && prettier --check ./docs/pages",
+    "check:consumer": "node scripts/check-consumer.mjs",
+    "check:release": "node scripts/check-release.mjs",
+    "format": "rescript format && oxfmt ./tests/index.js ./tests/fixtures.json ./tests/browser/native-api.spec.mjs ./tests/browser/describe-error.mjs ./tests/browser/server.mjs ./scripts/negative-fixtures.json ./playwright.config.mjs ./scripts/check-consumer.mjs ./scripts/check-release.mjs ./scripts/check-features.mjs ./scripts/check-features.test.mjs ./package.json ./docs && prettier --write .github/workflows/*.yml ./docs/pages",
+    "format:check": "rescript format --check && oxfmt ./tests/index.js ./tests/fixtures.json ./tests/browser/native-api.spec.mjs ./tests/browser/describe-error.mjs ./tests/browser/server.mjs ./scripts/negative-fixtures.json ./playwright.config.mjs ./scripts/check-consumer.mjs ./scripts/check-release.mjs ./scripts/check-features.mjs ./scripts/check-features.test.mjs ./package.json ./docs --check && prettier --check .github/workflows/*.yml ./docs/pages",
     "docs": "astro dev",
     "prebuild:docs": "node docs/llm.js",
     "build:docs": "astro build"
   },
   "devDependencies": {
     "@astrojs/starlight": "0.42.8",
+    "@playwright/test": "^1.64.1",
     "astro": "^7.2.9",
     "micromark": "^4.0.1",
     "oxfmt": "^0.75.0",
     "prettier": "^3.8.3",
     "prettier-plugin-astro": "^1.0.0",
-    "rescript": "^13.0.0-alpha.4",
+    "rescript": "13.0.0-alpha.5",
     "sharp": "^0.35.3"
   },
   "peerDependencies": {
-    "rescript": ">=13"
+    "rescript": ">=13.0.0-alpha.5 <13.0.0"
+  },
+  "overrides": {
+    "mdast-util-to-hast": "^13.2.1",
+    "postcss-selector-parser": "^6.1.5"
   }
 }
diff --git a/playwright.config.mjs b/playwright.config.mjs
new file mode 100644
index 00000000..66e6430e
--- /dev/null
+++ b/playwright.config.mjs
@@ -0,0 +1,16 @@
+import { defineConfig } from "@playwright/test";
+
+export default defineConfig({
+  testDir: "./tests/browser",
+  testMatch: "**/*.spec.mjs",
+  workers: 1,
+  reporter: "list",
+  use: {
+    browserName: "chromium",
+  },
+  webServer: {
+    command: "node tests/browser/server.mjs",
+    url: "http://127.0.0.1:4173",
+    reuseExistingServer: !process.env.CI,
+  },
+});
diff --git a/scripts/check-consumer.mjs b/scripts/check-consumer.mjs
new file mode 100644
index 00000000..ce2212fa
--- /dev/null
+++ b/scripts/check-consumer.mjs
@@ -0,0 +1,265 @@
+import { spawnSync } from "node:child_process";
+import { existsSync, mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { fileURLToPath, pathToFileURL } from "node:url";
+
+const repoRoot = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
+const packageJson = JSON.parse(readFileSync(path.join(repoRoot, "package.json"), "utf8"));
+const compilerVersion = "13.0.0-alpha.5";
+if (
+  packageJson.devDependencies.rescript !== compilerVersion ||
+  packageJson.peerDependencies.rescript !== ">=13.0.0-alpha.5 <13.0.0"
+) {
+  throw new Error("The tested compiler and package peer range are inconsistent.");
+}
+const requiredFiles = ["LICENSE", "README.md", "package.json", "rescript.json"];
+const forbiddenPaths = /^(?:tests|scripts|docs|\.github|node_modules|lib|dist)\//;
+
+const runCommand = (command, args, cwd) => {
+  const result = spawnSync(command, args, { cwd, encoding: "utf8" });
+  const output = `${result.stdout ?? ""}\n${result.stderr ?? ""}`;
+  if (result.error || result.status !== 0) {
+    throw new Error(`${command} ${args.join(" ")} failed.\n${result.error?.message ?? output}`);
+  }
+  return output;
+};
+
+const validateTarballFiles = (files) => {
+  const paths = files.map(({ path: filePath }) => filePath);
+  const missingFiles = requiredFiles.filter((filePath) => !paths.includes(filePath));
+  const invalidFiles = paths.filter(
+    (filePath) =>
+      forbiddenPaths.test(filePath) ||
+      (!requiredFiles.includes(filePath) &&
+        !(filePath.startsWith("src/") && /\.(?:res|resi)$/.test(filePath)) &&
+        filePath !== "LICENSE" &&
+        filePath !== "README.md"),
+  );
+  if (missingFiles.length > 0 || invalidFiles.length > 0) {
+    throw new Error(
+      `Unexpected package contents. Missing: ${missingFiles.join(", ") || "none"}. Unexpected: ${invalidFiles.join(", ") || "none"}.`,
+    );
+  }
+  if (!paths.some((filePath) => filePath.startsWith("src/") && filePath.endsWith(".res"))) {
+    throw new Error("The package tarball contains no ReScript source files.");
+  }
+  if (!paths.some((filePath) => filePath.startsWith("src/") && filePath.endsWith(".resi"))) {
+    throw new Error("The package tarball contains no ReScript interface files.");
+  }
+};
+
+const writeProject = (directory, sourceFile, features) => {
+  const sourceDirectory = path.join(directory, "src");
+  const fixturePath = path.resolve(repoRoot, sourceFile);
+  if (!fixturePath.startsWith(`${path.join(repoRoot, "scripts")}${path.sep}`)) {
+    throw new Error(`Consumer fixture must be under scripts/: ${sourceFile}`);
+  }
+  mkdirSync(sourceDirectory, { recursive: true });
+  writeFileSync(path.join(directory, "package.json"), '{"type":"module"}\n');
+  writeFileSync(
+    path.join(directory, "rescript.json"),
+    `${JSON.stringify(
+      {
+        name: "packed-webapi-consumer",
+        sources: [{ dir: "src" }],
+        dependencies:
+          features === null ? ["@rescript/webapi"] : [{ name: "@rescript/webapi", features }],
+        "experimental-features": { LetUnwrap: true },
+        warnings: { error: "+8" },
+        "package-specs": { module: "esmodule", "in-source": true },
+      },
+      null,
+      2,
+    )}\n`,
+  );
+  writeFileSync(path.join(sourceDirectory, "Consumer.res"), readFileSync(fixturePath));
+};
+
+const compilerCli = (directory) =>
+  path.join(directory, "node_modules", "rescript", "cli", "rescript.js");
+
+const compile = (directory, expectedFailure = null) => {
+  const cli = compilerCli(directory);
+  const clean = spawnSync(process.execPath, [cli, "clean"], { cwd: directory });
+  if (clean.status !== 0) {
+    throw new Error("Installed compiler failed to clean the consumer project.");
+  }
+  const result = spawnSync(process.execPath, [cli, "build", "--prod"], {
+    cwd: directory,
+    encoding: "utf8",
+  });
+  const output = `${result.stdout ?? ""}\n${result.stderr ?? ""}`
+    .replace(/\u001b\[[0-9;]*m/g, "")
+    .replace(/\s+/g, " ");
+  if (expectedFailure === null && result.status !== 0) {
+    throw new Error(`Consumer failed to compile:\n${output}`);
+  }
+  const diagnosticMatches =
+    expectedFailure instanceof RegExp
+      ? expectedFailure.test(output)
+      : typeof expectedFailure === "string" && output.includes(expectedFailure);
+  if (expectedFailure !== null && (result.status === 0 || !diagnosticMatches)) {
+    throw new Error(
+      `Consumer did not fail with the expected diagnostic ${expectedFailure}; exit status ${result.status}:\n${output}`,
+    );
+  }
+};
+
+const verifyUnsupportedCompiler = (directory, tarballPath) => {
+  mkdirSync(directory);
+  writeFileSync(path.join(directory, "package.json"), '{"type":"module"}\n');
+  const result = spawnSync(
+    "npm",
+    ["install", "--no-audit", "--no-fund", "--no-save", tarballPath, "rescript@12.3.1"],
+    { cwd: directory, encoding: "utf8" },
+  );
+  const output = `${result.stdout ?? ""}\n${result.stderr ?? ""}`;
+  if (
+    result.status === 0 ||
+    !output.includes("@rescript/webapi") ||
+    !output.includes(">=13.0.0-alpha.5 <13.0.0")
+  ) {
+    throw new Error(
+      `Unsupported compiler installation did not explain the peer constraint:\n${output}`,
+    );
+  }
+};
+
+const checkConsumers = async () => {
+  const tempDirectory = mkdtempSync(path.join(os.tmpdir(), "webapi-packed-consumer-"));
+  try {
+    const negativeOnly = process.argv.includes("--negative-only");
+    const suppliedArtifact = process.argv.slice(2).find((argument) => !argument.startsWith("--"));
+    let tarballPath;
+    let packagedFiles;
+    if (suppliedArtifact === undefined) {
+      const packOutput = runCommand(
+        "npm",
+        ["pack", "--json", "--pack-destination", tempDirectory],
+        repoRoot,
+      );
+      const [pack] = JSON.parse(packOutput);
+      tarballPath = path.join(tempDirectory, pack.filename);
+      packagedFiles = pack.files;
+    } else {
+      tarballPath = path.resolve(repoRoot, suppliedArtifact);
+      if (!existsSync(tarballPath)) {
+        throw new Error(`Packed artifact does not exist: ${tarballPath}`);
+      }
+      packagedFiles = runCommand("tar", ["-tzf", tarballPath], repoRoot)
+        .split(/\r?\n/)
+        .filter((filePath) => filePath.startsWith("package/"))
+        .map((filePath) => ({ path: filePath.slice("package/".length) }));
+    }
+    validateTarballFiles(packagedFiles);
+    const packedMetadata =
+      suppliedArtifact === undefined
+        ? packageJson
+        : JSON.parse(runCommand("tar", ["-xOf", tarballPath, "package/package.json"], repoRoot));
+    if (
+      packedMetadata.name !== packageJson.name ||
+      packedMetadata.version !== packageJson.version ||
+      !/^1\.0\.0-alpha\.[1-9]\d*$/.test(packedMetadata.version)
+    ) {
+      throw new Error(
+        "Packed artifact name/version does not match the explicit alpha package metadata.",
+      );
+    }
+    const publishLifecycleScripts = [
+      "prepare",
+      "prepack",
+      "prepublishOnly",
+      "publish",
+      "postpublish",
+    ];
+    const configuredPublishScripts = publishLifecycleScripts.filter(
+      (scriptName) => packedMetadata.scripts?.[scriptName] !== undefined,
+    );
+    if (configuredPublishScripts.length > 0) {
+      throw new Error(
+        `Packed artifact has lifecycle scripts that would execute during publish: ${configuredPublishScripts.join(", ")}.`,
+      );
+    }
+    const projectDirectory = path.join(tempDirectory, "project");
+    mkdirSync(projectDirectory);
+    writeFileSync(path.join(projectDirectory, "package.json"), '{"type":"module"}\n');
+    runCommand(
+      "npm",
+      [
+        "install",
+        "--no-audit",
+        "--no-fund",
+        "--no-save",
+        tarballPath,
+        `rescript@${compilerVersion}`,
+      ],
+      projectDirectory,
+    );
+    console.log(`[ok] installed tarball with supported ReScript ${compilerVersion}`);
+
+    verifyUnsupportedCompiler(path.join(tempDirectory, "unsupported"), tarballPath);
+    console.log("[ok] unsupported ReScript version rejected with peer-range diagnostic");
+
+    if (!negativeOnly) {
+      const scenarios = [
+        { name: "default", fixture: "scripts/consumer-default.res", features: null },
+        {
+          name: "Fetch-only",
+          fixture: "scripts/consumer-fetch.res",
+          features: ["WebAPI.Fetch"],
+        },
+        {
+          name: "SafeFetch",
+          fixture: "scripts/consumer-safe-fetch.res",
+          features: ["WebAPI.SafeFetch"],
+        },
+        {
+          name: "Fetch-only SafeFetch rejection",
+          fixture: "scripts/consumer-safe-fetch-disabled.res",
+          features: ["WebAPI.Fetch"],
+          expectedFailure: /The module or file (?:WebAPI\.)?SafeFetch can't be found\./,
+        },
+      ];
+
+      for (const scenario of scenarios) {
+        writeProject(projectDirectory, scenario.fixture, scenario.features);
+        compile(projectDirectory, scenario.expectedFailure ?? null);
+        console.log(`[ok] packed ${scenario.name} consumer`);
+      }
+
+      writeProject(projectDirectory, "scripts/consumer-runtime.res", ["WebAPI.Fetch"]);
+      compile(projectDirectory);
+      runCommand(
+        process.execPath,
+        [
+          "--input-type=module",
+          "--eval",
+          `await import(${JSON.stringify(pathToFileURL(path.join(projectDirectory, "src/Consumer.js")).href)})`,
+        ],
+        projectDirectory,
+      );
+      console.log(`[ok] packed consumer runtime using ReScript ${compilerVersion}`);
+    }
+
+    const negativeCases = JSON.parse(
+      readFileSync(path.join(repoRoot, "scripts/negative-fixtures.json"), "utf8"),
+    );
+    if (negativeOnly && negativeCases.length === 0) {
+      throw new Error("No negative consumer fixtures are registered.");
+    }
+    for (const negativeCase of negativeCases) {
+      writeProject(projectDirectory, negativeCase.fixture, negativeCase.features);
+      compile(projectDirectory, negativeCase.expectedDiagnostic);
+      console.log(`[ok] expected rejection: ${negativeCase.name}`);
+    }
+    console.log(`[ok] tarball contents (${packagedFiles.length} files)`);
+  } finally {
+    rmSync(tempDirectory, { recursive: true, force: true });
+  }
+};
+
+checkConsumers().catch((error) => {
+  console.error(error);
+  process.exitCode = 1;
+});
diff --git a/scripts/check-release.mjs b/scripts/check-release.mjs
new file mode 100644
index 00000000..283d9950
--- /dev/null
+++ b/scripts/check-release.mjs
@@ -0,0 +1,50 @@
+import { spawnSync } from "node:child_process";
+import { readFileSync } from "node:fs";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const repoRoot = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
+const packageJson = JSON.parse(readFileSync(path.join(repoRoot, "package.json"), "utf8"));
+const lockFile = JSON.parse(readFileSync(path.join(repoRoot, "package-lock.json"), "utf8"));
+const versionPattern = /^1\.0\.0-alpha\.[1-9]\d*$/;
+
+if (!versionPattern.test(packageJson.version)) {
+  throw new Error(`Expected an explicit 1.0.0-alpha.N version; received ${packageJson.version}.`);
+}
+if (
+  lockFile.version !== packageJson.version ||
+  lockFile.packages?.[""]?.version !== packageJson.version
+) {
+  throw new Error("package.json and package-lock.json versions must match.");
+}
+if (
+  packageJson.publishConfig?.access !== "public" ||
+  packageJson.publishConfig?.provenance !== true
+) {
+  throw new Error("Alpha packages must retain public access and provenance configuration.");
+}
+
+const packageReference = `${packageJson.name}@${packageJson.version}`;
+const published = spawnSync("npm", ["view", packageReference, "version"], {
+  cwd: repoRoot,
+  encoding: "utf8",
+});
+const registryOutput = `${published.stdout ?? ""}\n${published.stderr ?? ""}`;
+if (published.status === 0) {
+  throw new Error(`${packageReference} is already published; increment the alpha version.`);
+}
+if (!/\bE404\b|404 Not Found/.test(registryOutput)) {
+  throw new Error(`Unable to verify that ${packageReference} is unpublished:\n${registryOutput}`);
+}
+
+if (process.argv.includes("--publish")) {
+  if (process.env.GITHUB_REF !== "refs/heads/main") {
+    throw new Error("Real alpha publication is allowed only from refs/heads/main.");
+  }
+  if (process.env.GITHUB_EVENT_NAME !== "workflow_dispatch") {
+    throw new Error("Real alpha publication requires an explicit workflow_dispatch.");
+  }
+  console.log(`Verified unpublished alpha version ${packageReference} for the main branch.`);
+} else {
+  console.log(`Verified unpublished alpha version ${packageReference}; expected dist-tag: alpha.`);
+}
diff --git a/scripts/consumer-default.res b/scripts/consumer-default.res
new file mode 100644
index 00000000..0c13c244
--- /dev/null
+++ b/scripts/consumer-default.res
@@ -0,0 +1,3 @@
+let location = WebAPI.DOM.window->WebAPI.Window.location
+let href = location.href
+location->WebAPI.Location.reload
diff --git a/scripts/consumer-runtime.res b/scripts/consumer-runtime.res
new file mode 100644
index 00000000..8b2d0d8a
--- /dev/null
+++ b/scripts/consumer-runtime.res
@@ -0,0 +1,6 @@
+let headers = WebAPI.Headers.make()
+headers->WebAPI.Headers.set(~name="X-Artifact", ~value="installed")
+assert(headers->WebAPI.Headers.get("x-artifact")->Null.getOr("") == "installed")
+
+let response = WebAPI.Response.fromString("packed consumer")
+assert(await response->WebAPI.Response.text == "packed consumer")
diff --git a/scripts/fixtures/negative/DiagnosticMatching.res b/scripts/fixtures/negative/DiagnosticMatching.res
new file mode 100644
index 00000000..2bc68831
--- /dev/null
+++ b/scripts/fixtures/negative/DiagnosticMatching.res
@@ -0,0 +1 @@
+let invalidValue: int = "not an integer"
diff --git a/scripts/negative-fixtures.json b/scripts/negative-fixtures.json
new file mode 100644
index 00000000..3dec583c
--- /dev/null
+++ b/scripts/negative-fixtures.json
@@ -0,0 +1,8 @@
+[
+  {
+    "name": "expected compiler diagnostic matching",
+    "fixture": "scripts/fixtures/negative/DiagnosticMatching.res",
+    "features": null,
+    "expectedDiagnostic": "This has type: string"
+  }
+]
diff --git a/tests/FetchAPI/Headers__test.res b/tests/FetchAPI/Headers__test.res
index cb6ba06a..53f815f0 100644
--- a/tests/FetchAPI/Headers__test.res
+++ b/tests/FetchAPI/Headers__test.res
@@ -1,9 +1,11 @@
 let h = Headers.make()
 
 h->Headers.set(~name="X-Test", ~value="1")
+assert(h->Headers.get("x-test")->Null.getOr("") == "1")
 
 let h2 = Headers.fromDict(dict{"X-Vegetable": "Carrot"})
+assert(h2->Headers.get("x-vegetable")->Null.getOr("") == "Carrot")
 
 let h3 = Headers.fromKeyValueArray([("X-Fruit", "Apple"), ("X-Vegetable", "Carrot")])
-
-Console.log(h3->Headers.get("X-Fruit"))
+assert(h3->Headers.get("x-fruit")->Null.getOr("") == "Apple")
+assert(h3->Headers.has("x-vegetable"))
diff --git a/tests/FetchAPI/Request__test.res b/tests/FetchAPI/Request__test.res
index 23b1ee32..d790df70 100644
--- a/tests/FetchAPI/Request__test.res
+++ b/tests/FetchAPI/Request__test.res
@@ -1,5 +1,3 @@
-let req = Request.fromURL("https://example.com")
-
 let blob = Blob.make(~blobParts=[])
 let file = File.make(~fileBits=[], ~fileName="hello.txt")
 let params = URLSearchParams.fromString("greeting=hello")
@@ -28,4 +26,4 @@ let formDataReq = Request.fromURL(
 )
 let _formData: FormData.t = await formDataReq->Request.formData
 
-Console.log(await req2->Request.text)
+assert((await req2->Request.text) == "hello")
diff --git a/tests/FetchAPI/Response__test.res b/tests/FetchAPI/Response__test.res
index 04707902..0eb615d7 100644
--- a/tests/FetchAPI/Response__test.res
+++ b/tests/FetchAPI/Response__test.res
@@ -8,6 +8,7 @@ let stream = ReadableStream.make()
 let response = Response.fromNull(~init={status: 204, headers})
 
 let response1 = Response.fromString("pong", ~init={status: 200, headers})
+assert((await response1->Response.clone->Response.text) == "pong")
 
 let response2 = Response.fromBlob(blob)
 let response3 = Response.fromFile(file)
diff --git a/tests/FetchAPI/URLSearchParams__test.res b/tests/FetchAPI/URLSearchParams__test.res
index c4532c4d..e03c59a8 100644
--- a/tests/FetchAPI/URLSearchParams__test.res
+++ b/tests/FetchAPI/URLSearchParams__test.res
@@ -5,9 +5,7 @@ let params2 = URLSearchParams.fromKeyValueArray([("foo", "1"), ("bar", "b")])
 params2->URLSearchParams.values->Array.fromIterable->Array.forEach(Console.log)
 
 let params3 = URLSearchParams.fromDict(dict{"foo": "1", "bar": "b"})
-params3
-->URLSearchParams.entries
-->Array.fromIterable
-->Array.forEach(((key, value)) => Console.log2(key, value))
-
+assert(params3->URLSearchParams.get("foo")->Null.getOr("") == "1")
+assert(params3->URLSearchParams.has(~name="bar"))
 let paramStr = params3->URLSearchParams.toString
+assert(paramStr == "foo=1&bar=b" || paramStr == "bar=b&foo=1")
diff --git a/tests/URLAPI/URL__test.res b/tests/URLAPI/URL__test.res
index e9448152..48634645 100644
--- a/tests/URLAPI/URL__test.res
+++ b/tests/URLAPI/URL__test.res
@@ -1 +1,4 @@
 let url = URL.make(~url="/foo", ~base="https://bar.com")
+assert(url->URL.toJSON == "https://bar.com/foo")
+assert(URL.canParse(~url="/foo", ~base="https://bar.com"))
+assert(!URL.canParse(~url="not a URL"))
diff --git a/tests/browser/NativeAPI__test.res b/tests/browser/NativeAPI__test.res
new file mode 100644
index 00000000..a38aeaa1
--- /dev/null
+++ b/tests/browser/NativeAPI__test.res
@@ -0,0 +1,2 @@
+let url = URL.make(~url="/native", ~base="https://example.com")
+assert(url->URL.toJSON == "https://example.com/native")
diff --git a/tests/browser/describe-error.mjs b/tests/browser/describe-error.mjs
new file mode 100644
index 00000000..df3305c4
--- /dev/null
+++ b/tests/browser/describe-error.mjs
@@ -0,0 +1,42 @@
+const readProperty = (value, key) => {
+  try {
+    return typeof value === "object" && value !== null ? value[key] : undefined;
+  } catch {
+    return undefined;
+  }
+};
+
+const stringifySafely = (value) => {
+  try {
+    return String(value);
+  } catch {
+    return "<unprintable>";
+  }
+};
+
+export const describeError = (error) => {
+  const cause = readProperty(error, "Error");
+  const identity =
+    readProperty(error, "RE_EXN_ID") ?? readProperty(error, "name") ?? stringifySafely(error);
+  const message = readProperty(error, "message") ?? readProperty(cause, "message");
+  const stack = readProperty(error, "stack") ?? readProperty(cause, "stack");
+
+  let detail;
+  try {
+    detail = JSON.stringify(error, (_key, value) => {
+      if (value instanceof Error) {
+        return { name: value.name, message: value.message, stack: value.stack };
+      }
+      return typeof value === "bigint" ? `${value}n` : value;
+    });
+  } catch (serializationError) {
+    detail = `Exception payload omitted: ${stringifySafely(serializationError)}`;
+  }
+
+  return {
+    name: stringifySafely(identity),
+    message: message === undefined ? "" : stringifySafely(message),
+    stack: stack === undefined ? "" : stringifySafely(stack),
+    detail: detail ?? stringifySafely(error),
+  };
+};
diff --git a/tests/browser/index.html b/tests/browser/index.html
new file mode 100644
index 00000000..28150aec
--- /dev/null
+++ b/tests/browser/index.html
@@ -0,0 +1,14 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <script type="importmap">
+      {
+        "imports": {
+          "@rescript/runtime/": "/node_modules/@rescript/runtime/"
+        }
+      }
+    </script>
+  </head>
+  <body></body>
+</html>
diff --git a/tests/browser/native-api.spec.mjs b/tests/browser/native-api.spec.mjs
new file mode 100644
index 00000000..0d3910c5
--- /dev/null
+++ b/tests/browser/native-api.spec.mjs
@@ -0,0 +1,60 @@
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import { expect, test } from "@playwright/test";
+import path from "node:path";
+
+const currentDirectory = path.dirname(fileURLToPath(import.meta.url));
+const fixtures = JSON.parse(readFileSync(path.join(currentDirectory, "../fixtures.json"), "utf8"));
+
+test("browser runtime fixtures execute in Chromium", async ({ page }) => {
+  const errors = [];
+  page.on("pageerror", (error) => errors.push({ message: error.message, stack: error.stack }));
+  await page.goto("http://127.0.0.1:4173/tests/browser/index.html");
+  const results = await page.evaluate(async (paths) => {
+    const { describeError } = await import("/tests/browser/describe-error.mjs");
+    const outcomes = [];
+    for (const fixture of paths) {
+      try {
+        await import(`/tests/${fixture.replace(/\.res$/, ".js")}`);
+        outcomes.push({ fixture, _tag: "Success" });
+      } catch (error) {
+        outcomes.push({ fixture, _tag: "Failure", error: describeError(error) });
+      }
+    }
+    return outcomes;
+  }, fixtures.browserRuntime);
+  expect(fixtures.browserRuntime.length).toBeGreaterThan(0);
+  expect(results).toHaveLength(fixtures.browserRuntime.length);
+  expect(results.filter((result) => result._tag === "Failure")).toEqual([]);
+  expect(errors).toEqual([]);
+});
+
+test("browser error details preserve BigInt and cyclic ReScript failures", async ({ page }) => {
+  await page.goto("http://127.0.0.1:4173/tests/browser/index.html");
+  const failures = await page.evaluate(async () => {
+    const { describeError } = await import("/tests/browser/describe-error.mjs");
+    const bigIntFailure = describeError({
+      RE_EXN_ID: "Review_bigint",
+      _1: 1n,
+      Error: new Error("original BigInt failure"),
+    });
+    const cyclicPayload = {
+      RE_EXN_ID: "Review_cyclic",
+      Error: new Error("original cyclic failure"),
+    };
+    cyclicPayload._1 = cyclicPayload;
+    return {
+      bigIntFailure,
+      cyclicFailure: describeError(cyclicPayload),
+    };
+  });
+
+  expect(failures.bigIntFailure.name).toBe("Review_bigint");
+  expect(failures.bigIntFailure.message).toBe("original BigInt failure");
+  expect(failures.bigIntFailure.stack).toContain("original BigInt failure");
+  expect(failures.bigIntFailure.detail).toContain("1n");
+  expect(failures.cyclicFailure.name).toBe("Review_cyclic");
+  expect(failures.cyclicFailure.message).toBe("original cyclic failure");
+  expect(failures.cyclicFailure.stack).toContain("original cyclic failure");
+  expect(failures.cyclicFailure.detail).toContain("Exception payload omitted");
+});
diff --git a/tests/browser/server.mjs b/tests/browser/server.mjs
new file mode 100644
index 00000000..8f7c14b9
--- /dev/null
+++ b/tests/browser/server.mjs
@@ -0,0 +1,29 @@
+import { createServer } from "node:http";
+import { readFile } from "node:fs/promises";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "../..");
+const contentTypes = new Map([
+  [".html", "text/html"],
+  [".js", "text/javascript"],
+  [".mjs", "text/javascript"],
+]);
+
+createServer(async (request, response) => {
+  const pathname = new URL(request.url ?? "/", "http://localhost").pathname;
+  const file = path.resolve(root, `.${decodeURIComponent(pathname)}`);
+  if (!file.startsWith(`${root}${path.sep}`)) {
+    response.writeHead(403).end();
+    return;
+  }
+  try {
+    const content = await readFile(file);
+    response.writeHead(200, {
+      "content-type": contentTypes.get(path.extname(file)) ?? "application/octet-stream",
+    });
+    response.end(content);
+  } catch {
+    response.writeHead(404).end();
+  }
+}).listen(4173, "127.0.0.1");
diff --git a/tests/fixtures.json b/tests/fixtures.json
new file mode 100644
index 00000000..a9d90487
--- /dev/null
+++ b/tests/fixtures.json
@@ -0,0 +1,48 @@
+{
+  "compileOnly": [
+    "BindingAbsence__test.res",
+    "CanvasAPI/Path2D__test.res",
+    "CSSFontLoadingAPI/FontFace__test.res",
+    "DOMAPI/AddEventListener__test.res",
+    "DOMAPI/Document__test.res",
+    "DOMAPI/DOMMatrixReadOnly__test.res",
+    "DOMAPI/DOMMatrix__test.res",
+    "DOMAPI/Element__test.res",
+    "DOMAPI/EventTarget__test.res",
+    "DOMAPI/Event__test.res",
+    "DOMAPI/EventType__test.res",
+    "DOMAPI/HTMLCanvasElement__test.res",
+    "DOMAPI/HTMLElementHidden__test.res",
+    "DOMAPI/HTMLElement__test.res",
+    "DOMAPI/HTMLInputElement__test.res",
+    "DOMAPI/HTMLSlotElement__test.res",
+    "DOMAPI/ImageData__test.res",
+    "DOMAPI/Location__test.res",
+    "DOMAPI/SVGElement__test.res",
+    "DOMAPI/VideoFrame__test.res",
+    "FetchAPI/FormData__test.res",
+    "FileAPI/ReadableStream__test.res",
+    "IntersectionObserverAPI/IntersectionObserver__test.res",
+    "MediaCaptureAndStreamsAPI/MediaStream__test.res",
+    "MutationObserverAPI/MutationObserver__test.res",
+    "NotificationsAPI/Notification__test.res",
+    "ServiceWorkerAPI/ServiceWorker__test.res",
+    "WebAudioAPI/AudioDestinationNode__.test.res",
+    "WebAudioAPI/OfflineAudioContext__test.res",
+    "WebSocketsAPI/WebSocket__test.res",
+    "WebStorageAPI/Storage__test.res",
+    "WebWorkersAPI/SharedWorkerScope__test.res",
+    "WebWorkersAPI/SharedWorker__test.res"
+  ],
+  "documentationExamples": ["Fetch__test.res", "VisualViewport__test.res"],
+  "nodeRuntime": [
+    "DOMAPI/Classify__test.res",
+    "FetchAPI/Headers__test.res",
+    "FetchAPI/Request__test.res",
+    "FetchAPI/Response__test.res",
+    "FetchAPI/SafeFetch__test.res",
+    "FetchAPI/URLSearchParams__test.res",
+    "URLAPI/URL__test.res"
+  ],
+  "browserRuntime": ["browser/NativeAPI__test.res"]
+}
diff --git a/tests/index.js b/tests/index.js
index 1547bb4f..4803a803 100644
--- a/tests/index.js
+++ b/tests/index.js
@@ -1,4 +1,4 @@
-import { execFileSync, execSync, spawnSync } from "child_process";
+import { execSync, spawnSync } from "child_process";
 import * as fs from "fs";
 import { fileURLToPath, pathToFileURL } from "url";
 import * as path from "path";
@@ -10,16 +10,33 @@ const repoRoot = path.resolve(currentDir, "..");
 const testsDir = path.join(repoRoot, "tests");
 const rescriptConfig = JSON.parse(fs.readFileSync(path.join(repoRoot, "rescript.json"), "utf8"));
 const compiledSuffix = rescriptConfig.suffix ?? ".js";
+const fixtureCategories = JSON.parse(fs.readFileSync(path.join(testsDir, "fixtures.json"), "utf8"));
 
-const runtimeTests = [
-  "DOMAPI/Classify__test.res",
-  "FetchAPI/Headers__test.res",
-  "FetchAPI/Request__test.res",
-  "FetchAPI/Response__test.res",
-  "FetchAPI/SafeFetch__test.res",
-  "FetchAPI/URLSearchParams__test.res",
-  "URLAPI/URL__test.res",
-];
+const discoverFixtures = (directory, relativeDirectory = "") =>
+  fs.readdirSync(directory, { withFileTypes: true }).flatMap((entry) => {
+    const relativePath = path.join(relativeDirectory, entry.name);
+    const absolutePath = path.join(directory, entry.name);
+    if (entry.isDirectory()) {
+      return discoverFixtures(absolutePath, relativePath);
+    }
+    return entry.isFile() && entry.name.endsWith(".res") ? [relativePath] : [];
+  });
+
+const discoveredFixtures = discoverFixtures(testsDir)
+  .map((fixture) => fixture.split(path.sep).join("/"))
+  .sort();
+const categorizedFixtures = [
+  ...fixtureCategories.compileOnly,
+  ...fixtureCategories.documentationExamples,
+  ...fixtureCategories.nodeRuntime,
+  ...fixtureCategories.browserRuntime,
+].sort();
+if (JSON.stringify(discoveredFixtures) !== JSON.stringify(categorizedFixtures)) {
+  throw new Error(
+    `Fixture category mismatch.\nDiscovered: ${discoveredFixtures.join(", ")}\nCategorized: ${categorizedFixtures.join(", ")}`,
+  );
+}
+const runtimeTests = fixtureCategories.nodeRuntime;
 
 const compiledRuntimeTests = runtimeTests.map((testFile) =>
   testFile.replace(/\.res$/, compiledSuffix),
@@ -29,7 +46,6 @@ const compiledRuntimeTests = runtimeTests.map((testFile) =>
 execSync("npm run build", { cwd: repoRoot, stdio: "inherit" });
 
 const successGreen = "\x1b[32m";
-const warningYellow = "\x1b[33m";
 const errorRed = "\x1b[31m";
 const resetColor = "\x1b[0m";
 
@@ -62,20 +78,4 @@ for (const testFile of compiledRuntimeTests) {
   console.log(`${successGreen}✓ ${testFile}${resetColor}`);
 }
 
-// Assert generated test output stayed in sync.
-const gitDiff = execFileSync("git", ["ls-files", "--modified", "--", ...compiledRuntimeTests], {
-  cwd: testsDir,
-}).toString();
-if (!gitDiff) {
-  console.log(`${successGreen}✅ No unstaged generated test difference!${resetColor}`);
-  exit(0);
-} else {
-  console.log(
-    `${warningYellow}⚠️ There are unstaged differences in generated tests! Did you break a test?\n${gitDiff}${resetColor}`,
-  );
-  execFileSync("git", ["--no-pager", "diff", "--", ...compiledRuntimeTests], {
-    stdio: "inherit",
-    cwd: testsDir,
-  });
-  exit(1);
-}
+exit(0);