lesswrong-mcp

A read-only MCP server for LessWrong and the Alignment Forum. Through it, Claude can:

• search posts, comments, tags, users and sequences, sorted by relevance, date or karma, within a date range, on the Alignment Forum only, or inside one post's discussion
• read a post, in full
• read a post's whole discussion, answers on question posts included, or one comment
• list posts by author, tag, date range and karma in a stated order, or the posts that link to a post
• read a sequence in order

Both forums run on one ForumMagnum deployment, so one server reads both; Alignment Forum items are marked AF. It reads only public endpoints, so there's no API key or login.

Quick start

Claude Desktop

Download lesswrong-mcp.mcpb (always the newest release's bundle, also attached to the latest release) and double-click it, or install it from Settings → Extensions → Advanced settings → Install Extension…. The bundle uses Desktop's uv runtime, which installs Python and the dependencies for you.

To update, install the bundle from the latest release. If Settings → Extensions still shows the older version afterwards, remove the LessWrong & Alignment Forum extension there and install the new file again.

Claude Code

With uv installed:

claude mcp add --transport stdio --scope user lesswrong -- uvx --from git+https://github.com/seankessinger/lesswrong-mcp lesswrong-mcp

--scope user makes it available in every project; leave it out to add it to the current project only. Any other client that launches stdio servers can run the same uvx command.

What a call looks like

An illustrative listing, lw_filter_posts(tags=["interpretability-ml-and-ai"], after="2024-01-01", before="2024-12-31", af_only=true, limit=2):

# Posts (2) — tags=interpretability-ml-and-ai; 2024-01-01 to 2024-12-31; Alignment Forum only; sort=top

- [An example post title](https://www.lesswrong.com/api/post/AbCdEfGhIjKlMnOpQ) — Author Name (author-name) · karma 210 · 2024-03-14 · 31 comments · AF
- [Another example](https://www.lesswrong.com/api/post/QpOnMlKjIhGfEdCbA) — Second Author (second-author) · karma 155 · 2024-08-02 · 12 comments · AF

---
[More: call again with offset=2.]

Each row links what the other tools take: the post's id for lw_get_post, the author's slug for lw_filter_posts(author=...).

The tools

Tool	Takes	Returns
lw_search	query (quoted phrases are exact; -word excludes); types; sort (relevance, newest, oldest, karma); after/before; af_only; in_post; limit; page	Hits per kind, with the forum's totals and snippets
lw_get_post	post_id; max_chars (≤40,000); offset	The post as the forum's Markdown, in slices with the offset to continue from
lw_get_comments	post_id; comment_id; sort (top, new, old); max_chars; offset	The whole discussion (answers first on question posts, replies under their parents), or one comment
lw_filter_posts	author; tags; after/before; min_karma; af_only; sort (top, new, old); links_to; limit; offset	Matching posts; with links_to, the posts linking to that post
lw_get_sequence	sequence_id; max_chars; offset	The sequence's description and its posts in order

Posts, comments and sequences are named by their 17-character id, users and tags by slug. A value of the wrong shape, such as a link or a display name, is refused before any request, with advice on where the right value comes from.

Troubleshooting

Claude Desktop says "Could not connect to MCP server". There are two known causes, and on macOS the logs under ~/Library/Logs/Claude/ tell them apart:

• Desktop can't find uv. It runs this extension through uv, and main.log records the launch (look for the [UV Discovery] and [UV Runtime] lines). On macOS an app opened from the Dock or Finder gets the system's bare PATH, without ~/.local/bin or Homebrew, so a uv installed there can be invisible to it. Adding that directory to the PATH GUI apps inherit fixes it, e.g. sudo launchctl config user path "$HOME/.local/bin:/opt/homebrew/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin" and a reboot.
• The extension's display name contains a /. Desktop builds a log-file path from that name and refuses to connect a server whose name would escape it. main.log then reports a healthy connection, and the real error (path escape: "…") appears only in claude.ai-web.log. This bundle is named LessWrong & Alignment Forum; keep / out of display_name if you repackage it.

Development

It needs Python 3.11 or newer.

pip install -e '.[dev]'              # pytest, ruff, mypy
python -m lesswrong_mcp              # serve over stdio
pytest                               # hermetic: fakes the forum, no network
LW_LIVE_TESTS=1 pytest -m live       # opt-in: one read-only call per forum route and view
ruff check . && mypy lesswrong_mcp   # lint and type-check

Logging goes to stderr, never stdout, which carries the protocol. Retries and refused redirects are logged as warnings naming the request's path only.

Building the bundle

mkdir -p dist
npx @anthropic-ai/mcpb@2.1.2 pack . dist/lesswrong-mcp.mcpb

.mcpbignore is an allowlist: the bundle holds only manifest.json, pyproject.toml, LICENSE and the package.

The bundle ships unsigned. Don't run mcpb sign --self-signed on it: mcpb appends its signature block after the zip's end-of-central-directory record without recording it as a zip comment, so strict zip parsers, the desktop extension installer among them, reject the signed file (Invalid comment length … extra bytes at the end). Self-signing also only yields an "unverified publisher" bundle. For a trusted signature, use a CA-issued certificate (mcpb sign --cert/--key) and confirm the result still installs.

License

MIT