diff --git a/.github/workflows/CheckMarketplaceMetadata.yml b/.github/workflows/CheckMarketplaceMetadata.yml
new file mode 100644
index 0000000..a51b080
--- /dev/null
+++ b/.github/workflows/CheckMarketplaceMetadata.yml
@@ -0,0 +1,178 @@
+# The MIT License (MIT)
+#
+# Copyright © 2026 The pyTooling Authors
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
+# documentation files (the “Software”), to deal in the Software without restriction, including without limitation the
+# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit
+# persons to whom the Software is furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all copies or substantial portions of the
+# Software.
+#
+# THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+# WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+# COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+name: Check Marketplace Metadata
+
+on:
+  workflow_call:
+    inputs:
+      action_file:
+        description: |
+          Action metadata file. GitHub Marketplace requires it at the repository root.
+        type: string
+        required: false
+        default: 'action.yml'
+      description_limit:
+        description: |
+          Maximum length of the action's description. The Marketplace form rejects 'description' with
+          "Description must be less than 125 characters.", so the limit is exclusive.
+        type: number
+        required: false
+        default: 125
+      ubuntu_image:
+        description: 'Name of the Ubuntu image.'
+        type: string
+        required: false
+        default: 'ubuntu-26.04'
+
+  workflow_dispatch:
+
+jobs:
+  CheckMarketplaceMetadata:
+    name: 🛒 Check Marketplace metadata
+    runs-on: ${{ inputs.ubuntu_image || 'ubuntu-26.04' }}
+
+    steps:
+      - name: ⏬ Checkout repository
+        uses: actions/checkout@v7
+
+      - name: 🛒 Check the action's metadata against the Marketplace rules
+        id: check
+        shell: bash
+        env:
+          ACTION_FILE:        ${{ inputs.action_file || 'action.yml' }}
+          DESCRIPTION_LIMIT:  ${{ inputs.description_limit || 125 }}
+          REPOSITORY_PRIVATE: ${{ github.event.repository.private }}
+        run: |
+          # 🛒 Check the action's metadata against the Marketplace rules
+          set +e
+
+          ANSI_CYAN=$'\x1b[36m'
+          ANSI_LIGHT_RED=$'\x1b[91m'
+          ANSI_LIGHT_GREEN=$'\x1b[92m'
+          ANSI_LIGHT_YELLOW=$'\x1b[93m'
+          ANSI_NOCOLOR=$'\x1b[0m'
+
+          errors=0
+
+          fail() {
+            printf "%s\n" "${ANSI_LIGHT_RED}[FAILED]${ANSI_NOCOLOR}"
+            printf "  ↪ %s\n" "${ANSI_LIGHT_RED}${1}${ANSI_NOCOLOR}"
+            printf "::error title=%s::%s\n" "Marketplace" "${1}"
+            errors=$((errors + 1))
+          }
+
+          printf "%s\n" "${ANSI_CYAN}Checking '${ACTION_FILE}' against the GitHub Marketplace rules ...${ANSI_NOCOLOR}"
+
+          printf "%s" "Metadata file at the repository root ... "
+          if [[ ! -f "${ACTION_FILE}" ]]; then
+            fail "GitHub Marketplace requires an 'action.yml' or 'action.yaml' at the repository root; '${ACTION_FILE}' doesn't exist."
+            printf "::error title=%s::%s\n" "Marketplace" "Aborting: no metadata file to check."
+            exit 1
+          fi
+          printf "%s\n" "${ANSI_LIGHT_GREEN}[OK]${ANSI_NOCOLOR}"
+
+          # 'name', 'description' and 'branding' are read with the YAML parser rather than with grep, so a folded or
+          # quoted value is measured as the Marketplace sees it.
+          read -r -d '' script <<'PYTHON'
+          import sys, yaml
+          action = yaml.safe_load(open(sys.argv[1], encoding="utf-8")) or {}
+          branding = action.get("branding") or {}
+          # 'or ""' rather than a default: a key present with an empty value parses as None, and str(None) is the
+          # four-character string "None", which would pass every check below.
+          for key, value in (
+              ("name",        action.get("name") or ""),
+              ("description", action.get("description") or ""),
+              ("icon",        branding.get("icon") or ""),
+              ("color",       branding.get("color") or ""),
+          ):
+              print(f"{key}={str(value).strip()}")
+          PYTHON
+          metadata="$(python3 -c "${script}" "${ACTION_FILE}" 2>&1)"
+          if [[ $? -ne 0 ]]; then
+            fail "'${ACTION_FILE}' isn't valid YAML: ${metadata//$'\n'/ }"
+            exit 1
+          fi
+
+          name="$(       sed -n 's/^name=//p'        <<< "${metadata}")"
+          description="$(sed -n 's/^description=//p' <<< "${metadata}")"
+          icon="$(       sed -n 's/^icon=//p'        <<< "${metadata}")"
+          color="$(      sed -n 's/^color=//p'       <<< "${metadata}")"
+
+          printf "%s\n" ""
+          printf "  %-14s%s\n" "name:"        "${name}"
+          printf "  %-14s%s\n" "description:" "${description}"
+          printf "  %-14s%s\n" "icon:"        "${icon}"
+          printf "  %-14s%s\n" "color:"       "${color}"
+          printf "%s\n" ""
+
+          printf "%s" "Action name is set ... "
+          if [[ -z "${name}" ]]; then
+            fail "'name' is required. It also has to be unique across GitHub Marketplace, which can't be checked here."
+          else
+            printf "%s\n" "${ANSI_LIGHT_GREEN}[OK]${ANSI_NOCOLOR}"
+          fi
+
+          printf "%s" "Description is set ... "
+          if [[ -z "${description}" ]]; then
+            fail "'description' is required."
+          else
+            printf "%s\n" "${ANSI_LIGHT_GREEN}[OK]${ANSI_NOCOLOR}"
+
+            printf "%s" "Description is shorter than ${DESCRIPTION_LIMIT} characters ... "
+            length="$(printf "%s" "${description}" | wc -m)"
+            if [[ ${length} -ge ${DESCRIPTION_LIMIT} ]]; then
+              fail "'description' is ${length} characters; the Marketplace requires fewer than ${DESCRIPTION_LIMIT}."
+            else
+              printf "%s\n" "${ANSI_LIGHT_GREEN}[OK]${ANSI_NOCOLOR} (${length} characters)"
+            fi
+          fi
+
+          printf "%s" "Branding icon is set ... "
+          if [[ -z "${icon}" ]]; then
+            fail "'branding.icon' is required to list an action on the Marketplace."
+          elif [[ ! "${icon}" =~ ^[a-z0-9]+(-[a-z0-9]+)*$ ]]; then
+            fail "'branding.icon' is '${icon}', which isn't a Feather icon name."
+          else
+            printf "%s\n" "${ANSI_LIGHT_GREEN}[OK]${ANSI_NOCOLOR}"
+            # The accepted set is a subset of Feather, too long and too changeable to hard-code here, so the name is
+            # only checked for shape. A name that isn't in the set is rejected by the Marketplace form.
+            printf "  ↪ %s\n" "${ANSI_LIGHT_YELLOW}not verified against the Feather set — see https://feathericons.com${ANSI_NOCOLOR}"
+          fi
+
+          printf "%s" "Branding colour is one of the accepted values ... "
+          case "${color}" in
+            white|yellow|blue|green|orange|red|purple|gray-dark)
+              printf "%s\n" "${ANSI_LIGHT_GREEN}[OK]${ANSI_NOCOLOR}" ;;
+            "")
+              fail "'branding.color' is required to list an action on the Marketplace." ;;
+            *)
+              fail "'branding.color' is '${color}'; accepted are white, yellow, blue, green, orange, red, purple and gray-dark." ;;
+          esac
+
+          printf "%s" "Repository is public ... "
+          if [[ "${REPOSITORY_PRIVATE}" == "true" ]]; then
+            fail "The Marketplace only lists actions from public repositories."
+          else
+            printf "%s\n" "${ANSI_LIGHT_GREEN}[OK]${ANSI_NOCOLOR}"
+          fi
+
+          printf "%s\n" ""
+          if [[ ${errors} -ne 0 ]]; then
+            printf "%s\n" "${ANSI_LIGHT_RED}Counted ${errors} errors.${ANSI_NOCOLOR}"
+            exit 1
+          fi
+          printf "%s\n" "${ANSI_LIGHT_GREEN}No errors found.${ANSI_NOCOLOR}"
+          printf "%s\n" "${ANSI_LIGHT_YELLOW}Publishing itself is a checkbox when editing the release — there is no API for it.${ANSI_NOCOLOR}"
diff --git a/.github/workflows/Pipeline.yml b/.github/workflows/Pipeline.yml
index 7a23b12..886cf35 100644
--- a/.github/workflows/Pipeline.yml
+++ b/.github/workflows/Pipeline.yml
@@ -27,6 +27,9 @@ jobs:
   Prepare:
     uses: pyTooling/Actions/.github/workflows/PrepareJob.yml@r8
 
+  Marketplace:
+    uses: ./.github/workflows/CheckMarketplaceMetadata.yml
+
   DryRun:
     name: 🐧 Dry-run with a valid configuration
     runs-on: ubuntu-26.04
@@ -140,6 +143,7 @@ jobs:
     uses: pyTooling/Actions/.github/workflows/TagReleaseCommit.yml@r8
     needs:
       - Prepare
+      - Marketplace
       - DryRun
       - ErrorHandling
       - FailOnError
@@ -159,6 +163,7 @@ jobs:
     uses: ./.github/workflows/UpdateVersionBranch.yml
     needs:
       - Prepare
+      - Marketplace
       - DryRun
       - ErrorHandling
       - FailOnError
@@ -176,6 +181,7 @@ jobs:
     uses: pyTooling/Actions/.github/workflows/PublishReleaseNotes.yml@r8
     needs:
       - Prepare
+      - Marketplace
       - DryRun
       - ErrorHandling
       - FailOnError
diff --git a/README.md b/README.md
index 6d8cdab..5aa7d0d 100644
--- a/README.md
+++ b/README.md
@@ -322,6 +322,16 @@ three jobs, no token, no repository touched. Beyond that it releases itself, wit
   there; where nothing needs rewriting, the pull-request is a plain merge of `main`. Only **self**-references are
   touched — `pyTooling/Actions@r8` and `actions/checkout@v7` are separate decisions and are left alone.
 
+* **`CheckMarketplaceMetadata.yml`** — a local reusable workflow validating `action.yml` against the
+  [Marketplace](https://github.com/marketplace?type=actions) rules on every push: the metadata file at the repository
+  root, a name, a description shorter than 125 characters, a branding icon and one of the eight accepted branding
+  colours, and a public repository.
+
+  **Publishing itself stays manual.** There is no API for it — an action is listed by ticking *Publish this Action to
+  the GitHub Marketplace* while drafting or editing its release. A tag carries exactly one release, and the
+  Marketplace listing is a property of that release, not a second one, so an already-published release is **edited**
+  rather than re-created.
+
 So a release is one merge: open a `dev` → `main` pull-request titled `vMM.mm.pp`, write the release notes in its
 description, and merge it. What follows is automatic, except for the version-branch pull-request, which waits for a
 review.
diff --git a/action.yml b/action.yml
index 5ceb8b1..df3fc6f 100644
--- a/action.yml
+++ b/action.yml
@@ -19,7 +19,7 @@ name: 🔄 Synchronize Forked Repositories
 branding:
   icon: refresh-cw
   color: yellow
-description: Synchronize branches and tags of forked repositories of a GitHub organisation or user account with their upstream repositories.
+description: Synchronize branches and tags of forked repositories in a GitHub namespace with their upstream repositories.
 author: Patrick Lehmann (@Paebbels)
 
 inputs: