diff --git a/.claude-plugin/marketplace.json b/.claude-plugin/marketplace.json
index 488152f..2426006 100644
--- a/.claude-plugin/marketplace.json
+++ b/.claude-plugin/marketplace.json
@@ -8,7 +8,16 @@
   "plugins": [
     {
       "name": "basecamp",
-      "description": "Basecamp integration for Claude Code and Codex. Create todos, track work, link code to projects.",
+      "description": "Deprecated alias for basecamp-cli, kept so existing installs keep working. Install basecamp-cli instead, or run `basecamp setup` to switch.",
+      "source": {
+        "source": "url",
+        "url": "https://github.com/basecamp/basecamp-cli.git"
+      },
+      "category": "productivity"
+    },
+    {
+      "name": "basecamp-cli",
+      "description": "CLI-based Basecamp for Claude Code and Codex, driven by the basecamp command. Create todos, track work, link code to projects.",
       "source": {
         "source": "url",
         "url": "https://github.com/basecamp/basecamp-cli.git"
diff --git a/.github/workflows/check.yml b/.github/workflows/check.yml
new file mode 100644
index 0000000..4ab7259
--- /dev/null
+++ b/.github/workflows/check.yml
@@ -0,0 +1,18 @@
+name: Check
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  marketplace:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          persist-credentials: false
+      - run: bin/check-marketplace
diff --git a/README.md b/README.md
index b331003..036072c 100644
--- a/README.md
+++ b/README.md
@@ -14,9 +14,43 @@ claude plugin install <plugin-name>
 
 | Plugin | Description |
 |--------|-------------|
-| [basecamp](https://github.com/basecamp/basecamp-cli/tree/main/.claude-plugin) | Todos, cards, messages, files, schedule, check-ins, timeline, recordings, templates, webhooks, subscriptions, lineup, and campfire. |
+| [basecamp-cli](https://github.com/basecamp/basecamp-cli/tree/main/.claude-plugin) | Basecamp through the `basecamp` command, for Claude Code and Codex. Todos, cards, messages, files, schedule, check-ins, timeline, recordings, templates, webhooks, subscriptions, lineup, and campfire; links code to projects. |
+| [hey](https://github.com/basecamp/hey-cli) | Read email, manage todos, track time. |
+| [fizzy](https://github.com/basecamp/fizzy-cli) | Manage boards and cards, track work, link code to projects. |
 
-HEY and Fizzy plugins coming soon.
+### `basecamp` is now `basecamp-cli`
+
+The CLI plugin used to be `basecamp@37signals`. It's now
+`basecamp-cli@37signals`, with the same source, skills and hooks. The
+`basecamp` command itself keeps its name.
+
+For a deprecation window (7 days from the CLI release that ships the rename), `basecamp` stays in this
+marketplace as an alias with the same source as `basecamp-cli`. Existing
+installs keep loading and updating. From the basecamp-cli release with the
+rename on, a plugin installed under the old name says once that it has a
+new name. `basecamp setup` moves you to `basecamp-cli`. To
+do it by hand:
+
+```
+claude plugin marketplace update 37signals
+claude plugin install basecamp-cli@37signals
+claude plugin uninstall basecamp@37signals
+```
+
+The alias goes away in its own later PR, after the window.
+
+### The hosted Basecamp plugin
+
+`plugins/basecamp` is a second Basecamp plugin. It uses Basecamp's hosted
+connector at `https://mcp.basecamp.com/mcp` rather than the CLI, so it also
+works in claude.ai chat and Cowork. This is the folder Anthropic's plugin
+directory publishes as `basecamp`.
+
+This marketplace doesn't list it. `basecamp` here is the CLI alias until
+the window ends, and only after that can the name point at the hosted
+plugin. `bin/check-marketplace`, which CI runs, holds that rule: a
+`basecamp` entry passes only with exactly the same source as
+`basecamp-cli`. The script says when the rule can change.
 
 ## Development plugins
 
@@ -29,6 +63,15 @@ HEY and Fizzy plugins coming soon.
 
 ## About
 
-This repo is a thin marketplace index. Plugin source code (skills, hooks,
-commands) lives in each product's CLI repo. To contribute, open issues or PRs
-there.
+This repo is mostly a thin marketplace index. Plugin source code (skills,
+hooks, commands) lives in each product's own repo. To contribute, open issues
+or PRs there.
+
+The one plugin with files here, `plugins/basecamp` (the hosted plugin, not
+listed in the marketplace), is a mirror. Its source
+of truth is `plugins/claude/basecamp` in the (private) Basecamp connector
+repository, which tests it against the tools the connector actually serves.
+Don't edit the mirror; change it upstream, then run
+`bin/sync-basecamp-plugin <checkout>` to copy and validate it, and commit
+with the source commit it prints. `bin/sync-basecamp-plugin --check
+<checkout>` reports drift.
diff --git a/bin/check-marketplace b/bin/check-marketplace
new file mode 100755
index 0000000..2c53564
--- /dev/null
+++ b/bin/check-marketplace
@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+# Checks .claude-plugin/marketplace.json. Run by CI on every push and pull request.
+#
+# 1. It parses, and every plugin name is unique.
+# 2. A plugin named "basecamp", if listed, has exactly the same source as
+#    "basecamp-cli": a deprecated alias for it.
+#
+# "basecamp@37signals" used to be the CLI plugin, now "basecamp-cli". During the
+# deprecation window the alias keeps existing installs loading, and
+# basecamp-cli's `basecamp setup` moves them to basecamp-cli by key: it treats an
+# installed basecamp@37signals as the CLI plugin (basecamp/basecamp-cli#840).
+# Pointing "basecamp" anywhere else, such as the hosted plugin in
+# plugins/basecamp, would swap a different plugin in under existing installs,
+# and setup would uninstall it.
+#
+# Rule 2 changes only in its own PR, once both hold:
+#   - the deprecation window has passed (7 days from the CLI release that ships the rename), and
+#   - a basecamp-cli release has shipped that no longer treats basecamp@37signals
+#     as the old CLI plugin.
+# That PR first removes the alias. Pointing "basecamp" at the hosted plugin is a
+# later decision still.
+set -euo pipefail
+
+root="$(cd "$(dirname "$0")/.." && pwd)"
+marketplace="$root/.claude-plugin/marketplace.json"
+
+python3 - "$marketplace" <<'PY'
+import collections, json, sys
+
+with open(sys.argv[1]) as f:
+    plugins = json.load(f)["plugins"]
+names = [p["name"] for p in plugins]
+
+failed = False
+for name, count in collections.Counter(names).items():
+    if count > 1:
+        print(f"error: plugin name {name!r} is listed {count} times", file=sys.stderr)
+        failed = True
+
+by_name = {p["name"]: p for p in plugins}
+alias = by_name.get("basecamp")
+if alias is not None:
+    target = by_name.get("basecamp-cli")
+    if target is None or alias.get("source") != target.get("source"):
+        print(
+            "error: the 'basecamp' entry must be a deprecated alias with exactly the same source as\n"
+            "'basecamp-cli' until the deprecation window ends and a basecamp-cli release stops\n"
+            "treating basecamp@37signals as the old CLI plugin. See bin/check-marketplace.",
+            file=sys.stderr,
+        )
+        failed = True
+
+sys.exit(1 if failed else 0)
+PY
+echo "marketplace.json OK"
diff --git a/bin/sync-basecamp-plugin b/bin/sync-basecamp-plugin
new file mode 100755
index 0000000..9e00d4d
--- /dev/null
+++ b/bin/sync-basecamp-plugin
@@ -0,0 +1,60 @@
+#!/usr/bin/env bash
+# Mirror the hosted Basecamp plugin from basecamp-mcp-server, its source of truth.
+#
+#   bin/sync-basecamp-plugin <basecamp-mcp-server checkout>          copy, validate, print the source commit
+#   bin/sync-basecamp-plugin --check <basecamp-mcp-server checkout>  exit 1 if plugins/basecamp differs
+#
+# The source is plugins/claude/basecamp in that checkout. Sync from a clean
+# checkout of its main branch, and put the printed commit in the commit message.
+# Never edit plugins/basecamp here: change it upstream and sync.
+set -euo pipefail
+
+check=0
+if [[ "${1:-}" == "--check" ]]; then
+  check=1
+  shift
+fi
+
+if [[ $# -ne 1 ]]; then
+  sed -n '4,5p' "$0" | sed 's/^# *//' >&2
+  exit 2
+fi
+
+root="$(cd "$(dirname "$0")/.." && pwd)"
+upstream="$(cd "$1" && pwd)"
+src="$upstream/plugins/claude/basecamp"
+dest="$root/plugins/basecamp"
+
+if [[ ! -f "$src/.claude-plugin/plugin.json" ]]; then
+  echo "error: $src is not the Basecamp plugin (no .claude-plugin/plugin.json)" >&2
+  exit 2
+fi
+
+if [[ $check -eq 1 ]]; then
+  if diff -r "$src" "$dest"; then
+    echo "plugins/basecamp matches $(git -C "$upstream" rev-parse --short HEAD)"
+  else
+    echo "plugins/basecamp has drifted from basecamp-mcp-server; run bin/sync-basecamp-plugin" >&2
+    exit 1
+  fi
+  exit 0
+fi
+
+if [[ -n "$(git -C "$upstream" status --porcelain -- plugins/claude/basecamp)" ]]; then
+  echo "error: uncommitted changes under $src; sync from a committed source" >&2
+  exit 2
+fi
+
+rm -rf "$dest"
+mkdir -p "$dest"
+cp -R "$src/." "$dest/"
+find "$dest" -name .DS_Store -delete
+
+if command -v claude >/dev/null 2>&1; then
+  claude plugin validate "$dest"
+else
+  echo "claude not installed; skipping claude plugin validate" >&2
+fi
+
+echo
+echo "Mirrored from basecamp/basecamp-mcp-server@$(git -C "$upstream" rev-parse HEAD)"
diff --git a/plugins/basecamp/.claude-plugin/plugin.json b/plugins/basecamp/.claude-plugin/plugin.json
new file mode 100644
index 0000000..0468464
--- /dev/null
+++ b/plugins/basecamp/.claude-plugin/plugin.json
@@ -0,0 +1,21 @@
+{
+  "name": "basecamp",
+  "displayName": "Basecamp",
+  "version": "0.1.0",
+  "description": "Work in your Basecamp projects from Claude: catch up on a project, recap your week, triage your Hey! menu, plan work into to-dos and cards, draft a check-in answer, and prep for a meeting, through Basecamp's own hosted connector.",
+  "author": {
+    "name": "37signals",
+    "email": "support@37signals.com",
+    "url": "https://basecamp.com"
+  },
+  "homepage": "https://basecamp.com",
+  "repository": "https://github.com/basecamp/claude-plugins",
+  "license": "MIT",
+  "keywords": [
+    "basecamp",
+    "projects",
+    "to-dos",
+    "project management",
+    "check-ins"
+  ]
+}
diff --git a/plugins/basecamp/.mcp.json b/plugins/basecamp/.mcp.json
new file mode 100644
index 0000000..3a30f34
--- /dev/null
+++ b/plugins/basecamp/.mcp.json
@@ -0,0 +1,8 @@
+{
+  "mcpServers": {
+    "basecamp": {
+      "type": "http",
+      "url": "https://mcp.basecamp.com/mcp"
+    }
+  }
+}
diff --git a/plugins/basecamp/README.md b/plugins/basecamp/README.md
new file mode 100644
index 0000000..2790cdf
--- /dev/null
+++ b/plugins/basecamp/README.md
@@ -0,0 +1,58 @@
+# Basecamp
+
+Bring your Basecamp projects into Claude. Ask what happened on a project
+while you were out, what's on your plate this week, or what a long thread
+actually decided. Then have Claude do the follow-through: add and assign
+to-dos, move cards, post a comment, draft a check-in answer, write up an
+agenda.
+
+This plugin pairs Basecamp's own hosted connector with a skill for working
+in Basecamp and six ready-made workflows.
+
+## Get started
+
+1. Add the plugin, then open its **Connectors** tab and connect Basecamp.
+2. Sign in to Basecamp and choose **Full access**, or **Read-only** if you
+   only want Claude to read.
+3. Ask away: "What's assigned to me in Basecamp this week?"
+
+You need a Basecamp account. There's no extra charge.
+
+## Workflows
+
+In Cowork and Claude Code, run them as commands. In chat, just ask, and
+Claude picks the one that fits.
+
+| Command | What it does |
+| --- | --- |
+| `/basecamp:catch-up <project>` | What changed on a project, what was decided, what's open, and what needs you |
+| `/basecamp:weekly-recap` | What you finished, what moved across your projects, and what's next week |
+| `/basecamp:triage-hey` | Sorts your Hey! menu into needs-you, worth-knowing, and nothing-to-do, with draft replies |
+| `/basecamp:plan-project <project> <goal>` | Turns a goal or notes into to-do lists or cards with owners and dates |
+| `/basecamp:draft-check-in [question]` | Drafts your answer to an automatic check-in from what you actually did |
+| `/basecamp:meeting-prep <project> <topic>` | A one-page brief and agenda from the project's recent activity |
+
+Claude shows you a plan or a draft before it creates or posts anything,
+and every workflow that only reads leaves your Basecamp untouched.
+
+## What it can work with
+
+Projects and the people on them; to-dos and to-do lists; messages,
+comments and boosts; Card Tables, cards and steps; schedules; Docs & Files;
+Campfire chats and Pings; automatic check-ins; your assignments and Hey!
+menu; and search across your account.
+
+## Your data
+
+The plugin connects to one place, Basecamp's hosted connector at
+`https://mcp.basecamp.com/mcp`, run by 37signals. It acts as you: Claude
+sees only what you can see in Basecamp and can change only what you can
+change there. The plugin itself is instructions and stores nothing; the
+connector passes Claude's requests to Basecamp's API on your behalf. Most
+things you remove go to the Basecamp trash, where
+they can be restored. Disconnect any time from the plugin's Connectors tab
+or from Connected apps in your Basecamp profile menu.
+
+- Privacy policy: https://37signals.com/policies/privacy
+- Terms: https://37signals.com/policies/terms
+- Support: https://basecamp.com/support
diff --git a/plugins/basecamp/commands/catch-up.md b/plugins/basecamp/commands/catch-up.md
new file mode 100644
index 0000000..2bd47c3
--- /dev/null
+++ b/plugins/basecamp/commands/catch-up.md
@@ -0,0 +1,37 @@
+---
+description: Catch up on a Basecamp project — what changed, what was decided, what's still open, and what needs you.
+argument-hint: <project name or link>
+---
+
+# Catch up on a project
+
+The project to catch up on: $ARGUMENTS
+
+1. **Find the project.** A link: `get_by_url`. A name: `list_projects`, or
+   `search` if the list is long. If several match, ask which; if none was
+   named, ask.
+2. **Read what happened.** `get_project_timeline` for the recent activity.
+   It returns the latest 100 events and can't page, so if its oldest event
+   is newer than the start of the window, say the catch-up starts there.
+   `get_project` for its dock, then `list_messages` on its message board for
+   the latest discussions. Open what matters with `get_by_url` on its
+   `app_url`: a decision, a long thread, a document that changed.
+3. **Who's asking.** `get_me` names the person, so you can tell what's
+   theirs.
+4. **What's open now.** The timeline only shows what moved recently, so read
+   current state too, keeping this project's group from each:
+   `list_everything_todos` with `state` set to overdue, then to unassigned;
+   `list_everything_cards` with `state` set to overdue; and `get_my_assignments`
+   for what's on them.
+
+Reply in four short parts, linking every item to its `app_url`:
+
+- **What changed** in about the last week, or since the date they give: the
+  handful of things that matter, not every event.
+- **Decided:** each decision, quoting the line that settled it.
+- **Open:** unanswered questions, overdue or unassigned to-dos, stuck cards.
+- **Needs you:** what's assigned to them, mentions them, or waits on their
+  answer.
+
+This is a read: post nothing and change nothing. Offer to dig into any
+thread.
diff --git a/plugins/basecamp/commands/draft-check-in.md b/plugins/basecamp/commands/draft-check-in.md
new file mode 100644
index 0000000..88856f1
--- /dev/null
+++ b/plugins/basecamp/commands/draft-check-in.md
@@ -0,0 +1,33 @@
+---
+description: Draft your answer to a Basecamp automatic check-in, like "What did you work on this week?", from your own recent activity.
+argument-hint: "[check-in question link or project]"
+---
+
+# Draft a check-in answer
+
+Which check-in: $ARGUMENTS
+
+1. **Find the question.** A link: `get_by_url`. A project: `get_project`
+   for its dock, then `get_questionnaire` and `list_questions`. If they
+   didn't say, ask which check-in.
+2. **Read their voice.** `get_me`, then `get_answers_by_person` with the
+   question and their `person_id` for their last few answers: length, tone,
+   format.
+3. **Gather what they did** over the question's period (a week, unless the
+   question says otherwise): `get_catchup` with `days` (its finished to-dos
+   are scoped to that window), and `get_project_timeline` on the projects
+   they were active in. Timelines and the catch-up's activity counts include
+   teammates' work: count an event as theirs only when its creator is the
+   person from `get_me`, and use the rest as context. `get_catchup` reaches back 14 days at most, so for a
+   longer period, such as a monthly check-in, say the draft covers only the
+   last 14 days. `get_my_completed_assignments` carries no completion dates,
+   so don't count its items as done in this period. For what's in
+   progress, next, and blocked, read `get_my_assignments`: current work
+   with no recent activity shows up only there.
+
+Draft the answer the way they write: what they finished, what's in
+progress, what's next, and anything blocked, linking to the work. Show the
+draft and ask what to change.
+
+Post only when they say to: `create_answer` with the question and the
+answer as HTML in `content`. Then link to it.
diff --git a/plugins/basecamp/commands/meeting-prep.md b/plugins/basecamp/commands/meeting-prep.md
new file mode 100644
index 0000000..08fec1c
--- /dev/null
+++ b/plugins/basecamp/commands/meeting-prep.md
@@ -0,0 +1,37 @@
+---
+description: Prep for a meeting about a Basecamp project — recent decisions, open questions, what's late, and a draft agenda.
+argument-hint: <project name or link, and the meeting's topic>
+---
+
+# Prep for a meeting
+
+The project and the meeting: $ARGUMENTS
+
+1. **Find the project.** A link: `get_by_url`. A name: `list_projects` or
+   `search`. If none was named, ask.
+2. **Read the state of things.**
+   - `get_project_timeline` for what happened since the last meeting (a
+     week, unless they say). It returns the latest 100 events and can't
+     page; if they don't reach back that far, say where the brief starts.
+   - `get_project` for its dock, then `list_messages` on its message board,
+     and `get_by_url` on the threads that matter.
+   - Open work: `list_todolists` and `list_todos`, or `get_card_table`, for
+     what's overdue, unassigned, or stuck.
+   - `get_upcoming_schedule` from today to two weeks out for dates coming
+     up, keeping this project's entries and recurring occurrences.
+     `list_schedule_entries` lists a recurring series once, at its first
+     date, so it misses the next meeting of a series.
+   - `search` for the meeting's topic, to find the docs and threads behind
+     it.
+
+Reply with a one-page brief, linking every item to its `app_url`:
+
+- **Since last time:** decisions and changes, a line each.
+- **Open questions:** each with who raised it.
+- **At risk:** what's late or blocked, and who owns it.
+- **Agenda:** five or fewer items, in order, each with the decision the
+  meeting needs to make.
+
+If they want it in Basecamp, offer to save the agenda as a document
+(`create_document` in the project's Docs & Files, `vault_id` from the
+dock), as a draft unless they say to publish it.
diff --git a/plugins/basecamp/commands/plan-project.md b/plugins/basecamp/commands/plan-project.md
new file mode 100644
index 0000000..864e456
--- /dev/null
+++ b/plugins/basecamp/commands/plan-project.md
@@ -0,0 +1,34 @@
+---
+description: Turn a goal, brief, or meeting notes into a Basecamp plan — to-do lists and to-dos with owners and dates, or cards on a Card Table.
+argument-hint: <project name or link, and what to plan>
+---
+
+# Plan it in Basecamp
+
+What to plan, and where: $ARGUMENTS
+
+1. **Find the project.** A link: `get_by_url`. A name: `list_projects` or
+   `search`. If none fits, offer to create one with `create_project`, and
+   only create it once they agree.
+2. **Read its dock.** `get_project` lists its tools. Plan into to-dos unless
+   they asked for cards or the project works from a Card Table
+   (`get_card_table` shows its columns).
+3. **Find the people.** `list_project_people` for who can own each piece.
+   Don't guess an owner they didn't name.
+4. **Propose the plan first**, as an outline: lists (or columns) with their
+   to-dos (or cards), each with an owner and a due date where one is clear.
+   Ask what to change.
+5. **Create it once they approve.**
+   - To-dos: `create_todolist` in the project's to-do set (`todoset_id` from
+     the dock), then `create_todo` for each, with `assignee_ids` and
+     `due_on` (`YYYY-MM-DD`).
+   - Cards: `create_card` in the right column (`column_id`), then
+     `update_card` to set `assignee_ids`.
+   For to-dos, leave `notify` off unless they want people notified now.
+   Cards can't do that: `create_card` takes no assignees, so its `notify`
+   reaches no one, and `update_card` has no `notify`. If they want card
+   owners told, say so and offer to post or comment instead.
+
+Reply with what was created, linked, and anything you skipped and why. The
+`posting-and-mentions` topic of `get_basecamp_guide` says who each post
+notifies.
diff --git a/plugins/basecamp/commands/triage-hey.md b/plugins/basecamp/commands/triage-hey.md
new file mode 100644
index 0000000..56ec5a6
--- /dev/null
+++ b/plugins/basecamp/commands/triage-hey.md
@@ -0,0 +1,28 @@
+---
+description: Triage your Basecamp Hey! menu — sort what needs a reply from what's just FYI, draft replies, and clear what's handled.
+---
+
+# Triage my Hey!
+
+1. `get_my_notifications`: unreads first. Unreads come back in one list,
+   capped at 100; `page` pages only the read items, so it can't fetch more
+   unreads. If the list is full, say there may be more.
+2. Open anything you can't judge from its excerpt with `get_by_url` on its
+   `app_url`.
+3. Sort each unread into one of three groups:
+   - **Needs you:** a direct question, a mention asking for something, an
+     assignment, a decision waiting on them.
+   - **Worth knowing:** announcements and updates on their work.
+   - **Nothing to do:** boosts, automatic notices, threads that already
+     moved on.
+
+Reply with the three groups, each item a line with who, the project, the
+gist, and a link. For **Needs you**, offer a short draft reply for each.
+
+Act only when the person says so:
+
+- **Reply:** `get_by_url` on the item gives the `reply_target`; post the
+  reply there, quoting it back to them first. Use `mentions` with person IDs
+  to @-mention someone. No `reply_target` means a reply can't be posted from
+  here; say so.
+- **Clear:** `mark_as_read` with the `readables` of the items they choose.
diff --git a/plugins/basecamp/commands/weekly-recap.md b/plugins/basecamp/commands/weekly-recap.md
new file mode 100644
index 0000000..6f6c1b9
--- /dev/null
+++ b/plugins/basecamp/commands/weekly-recap.md
@@ -0,0 +1,35 @@
+---
+description: Recap your week in Basecamp — what you finished, what moved across your projects, and what's coming up next week.
+argument-hint: "[days back, up to 14]"
+---
+
+# Recap my week
+
+How far back: $ARGUMENTS (a number of days, up to 14; a week if nothing was
+given).
+
+1. `get_catchup` with `days` for announcements, to-dos assigned to and
+   completed by the person, their overdue to-dos, and activity by project.
+2. `get_my_assignments` for what's still on their plate. For what they
+   finished, use only the catch-up's completed to-dos: they're the person's
+   own and scoped to the window. Project timelines include teammates'
+   completions, and `get_my_completed_assignments` has no dates. The
+   catch-up's to-dos carry no `app_url`: `get_todo` on each one you list
+   gives the link.
+3. `get_upcoming_schedule` with `start_date` today and `end_date` a week out
+   for what's next. It covers the whole account, so keep only entries and
+   recurring occurrences whose participants include the person (`get_me`
+   names them).
+4. For the two or three busiest projects in the catch-up, `get_project_timeline`
+   to say what actually moved, not just how much.
+
+Reply with:
+
+- **Done:** what they finished in the window, grouped by project.
+- **Moved:** the notable changes in their projects, a line each.
+- **Still open:** overdue first, then what's due next week.
+- **Coming up:** schedule entries next week.
+
+Link every item to its `app_url`, name the project, and keep it to what a
+person would read in two minutes. If they want to share it, offer to draft
+it as a check-in answer or a message, and post only once they say so.
diff --git a/plugins/basecamp/skills/basecamp/SKILL.md b/plugins/basecamp/skills/basecamp/SKILL.md
new file mode 100644
index 0000000..c135cb9
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+++ b/plugins/basecamp/skills/basecamp/SKILL.md
@@ -0,0 +1,86 @@
+---
+name: basecamp
+description: Work with Basecamp through the Basecamp tools — find, read, create, and update projects, to-dos, cards, messages, comments, documents, schedules, and Campfire chats. Use for any Basecamp question or action, and for any basecamp.com link.
+---
+
+# Basecamp
+
+Every Basecamp action is its own tool, named for what it does: `get_*` and
+`list_*` read; `create_*`, `update_*`, `complete_*`, `move_*`, `trash_*` and
+the rest change data. Everything runs as the signed-in person and sees only
+what they can see.
+
+The server keeps the reference notes on how Basecamp works:
+`get_basecamp_guide` returns the core concepts with no `topic`, or one
+topic — `concepts` (accounts, projects, the dock, and the IDs each tool
+takes), `finding-things`, `my-work`, `posting-and-mentions` (HTML, mentions,
+who is notified), and `deleting-and-trash`. Read the topic before a task it
+covers that you have not done in this conversation.
+
+## Where to start
+
+- **A Basecamp link?** Pass it to `get_by_url` as `url`. It returns the IDs
+  the link names, the record itself, and, for anything that takes comments
+  when this connection can post them, `reply_target`: the tool and IDs a
+  reply goes to. A link to a comment answers with the comment and its
+  parent as the reply target, since comments are not threaded. No
+  `reply_target` means no reply can be posted from here. Don't read IDs out
+  of the link yourself.
+- **By keyword?** `search`, then `get_by_url` with a result's `app_url` for
+  the full record.
+- **Mine?** `get_my_assignments` (priorities first), `get_my_day` (today's
+  schedule and due to-dos), `get_overdue_todos`, `get_upcoming_schedule`,
+  `get_my_notifications` (the Hey! menu: unreads first), `get_catchup`
+  (what happened while away).
+- **In a project?** `list_projects` or `search` to find it, then
+  `get_project` for its dock: each dock tool's ID is what that tool's
+  `list_*` and `create_*` calls take.
+- **Long results** come a page at a time. A result carrying `next_cursor`
+  or `next_page` has more: pass that value back as `cursor` or `page` to
+  continue.
+
+## Accounts and projects
+
+Each connection works in one Basecamp account; `get_me` names the
+signed-in person and that account. A link into another account is out of
+reach from this connection — `get_by_url` says so; tell the person rather
+than guess. When a request needs a project and doesn't name one, ask which
+— don't pick one for them.
+
+## Writing
+
+- **Rich text** — message bodies, comments, documents, to-do and card notes
+  — is HTML; titles, to-do names and Campfire lines are plain text. The
+  `posting-and-mentions` topic lists the tags Basecamp keeps.
+- **@-mentions.** `create_comment` takes `mentions`: person IDs from
+  `list_pingable_people` or `list_project_people`.
+- **Assigning.** `assignee_ids` replaces the whole list; include everyone
+  who stays assigned. Dates are `YYYY-MM-DD`.
+- **Notifications.** Posting can notify people, but not always: a message
+  or document created without `status: "active"` is an unposted draft, and
+  a to-do or event notifies only when `notify` is true. The
+  `posting-and-mentions` topic says who each post notifies; report what was
+  actually sent. Confirm with the person before posting on their behalf to
+  others, and quote what will be posted.
+
+## Removing things
+
+`trash_*` tools move an item to the Basecamp trash, where it can be
+restored. Tools whose description says "Permanently" cannot be undone: run
+one only when the person asked for exactly that deletion. The
+`deleting-and-trash` topic covers the difference, and archiving.
+
+## Replying well
+
+Link to what you mention: every item carries an `app_url`. Name the project
+and, when the person has several accounts, the account. Say plainly when
+something could not be found or read rather than filling the gap.
+
+**Say what your reads covered.** Every summary, recap, brief or triage
+states what its reads did and didn't cover, and never claims more than was
+fetched. Reads stop short in known ways: a result marked truncated, a
+timeline that ends at its latest 100 events, a window capped at 14 days, an
+undated list, a thread whose comments you didn't open, records that include
+other people's work. When one applies, say so in the reply ("Done covers
+to-dos only", "the timeline reaches back to Tuesday") instead of presenting
+the section as complete.