The full upstream README, mirrored here for reference. Install config, tool schemas, adoption signals, and an original overview live on the Relay MCP listing page.
This repo is the open-source reference implementation. The author runs a private deployed instance at a different URL, but you should deploy your own instance for production use.
A self-hosted session relay for Claude. When you work across multiple Claude surfaces (Code, Cowork, Claude.ai connectors), each surface lives in its own context window. The relay gives them a shared message thread they can all post to and read from, so a Code session can hand state to a Chat session without copy-paste, and a scheduled Cowork task can leave a note your morning Chat picks up. It is a lightweight whiteboard, not a log or a memory store.
The server exposes six MCP tools.
| Tool | Description |
|---|---|
relay_list_threads | List threads with last activity and message count. |
relay_create_thread | Create a named thread. |
relay_post_message | Post a message to a thread. Auto-creates the thread if missing. |
relay_read_thread | Read recent messages, newest first. Optional cursor update. |
relay_check_new | Return only messages since this reader last checked. |
relay_archive_thread | Soft-archive a thread. History is preserved. |
Every message carries a surface field (chat, cowork, code, other) and an optional free-text session_tag so threads stay legible across many parallel sessions.
Cloudflare Worker at src/index.ts. Stateless. Speaks streamable HTTP MCP at /mcp.
Supabase Postgres for thread, message, and read-cursor storage. Three tables, all prefixed relay_. RLS enabled with zero policies; only the Worker's service-role key can read or write.
Two auth paths on the same server:
Authorization: Bearer <RELAY_API_KEY>. Simplest possible. No browser flow./.well-known/oauth-authorization-server, /register, /authorize, and /token. Access tokens are HS256 JWTs signed with RELAY_API_KEY. Stateless, no KV or Durable Objects required. Access tokens last 90 days, refresh tokens 365.See Security for the consolidated auth, rotation, and threat-model writeup.
Single tenant in v1. The Worker reads a hardcoded user UUID from the RELAY_USER_ID secret. Multi-user support is a one-file change in src/oauth.ts plus an RLS policy migration; the schema already carries user_id columns.
Self-hosting takes about ten minutes. You will need a Cloudflare account (Workers free tier is fine), a Supabase project, and Node 20+ locally.
Create a new project at supabase.com. In the SQL editor, paste and run migrations/001_initial.sql. This creates relay_threads, relay_messages, relay_read_cursors, sets up indexes, enables RLS with zero policies, and revokes anon and authenticated grants.
From Project Settings → API, copy:
https://abcdef.supabase.co).Generate one (uuidgen, crypto.randomUUID(), or any UUID v4 generator). This is the single user the v1 server is bound to. You can rotate it later, but everything posted under one UUID is invisible under another.
Wrangler prints the deployed URL, something like https://relay-mcp.<your-subdomain>.workers.dev. That URL plus /mcp is the MCP endpoint.
Edit wrangler.toml and uncomment the routes block, swapping relay-mcp.example.com for a hostname on a Cloudflare zone you own. Re-run npx wrangler deploy. Wrangler creates the CNAME automatically.
Forty assertions, including the OAuth flow. All green means you are live.
Replace <RELAY_URL> with your deployed URL and <RELAY_API_KEY> with the secret you set above.
Add to .mcp.json in the project root, or to ~/.claude.json for global access.
Restart Claude Code, run /mcp, and confirm relay appears with six tools.
Add to .cursor/mcp.json in the project root, or to ~/.cursor/mcp.json for global access.
Restart Cursor, open the MCP settings, and confirm relay appears with six tools.
Gotcha: the relay block must sit inside the mcpServers object. Cursor silently ignores any server defined at the top level of the file. If the tools do not show up, this is the first thing to check.
Add an mcp_servers block to any task prompt that needs relay access.
Claude Desktop's MCP support expects stdio commands, not remote HTTP URLs. To connect to a remote relay, use the mcp-remote bridge, which adapts a stdio-launched process to a remote HTTP MCP server.
Open claude_desktop_config.json (on Windows: %APPDATA%\Claude\claude_desktop_config.json; on macOS: ~/Library/Application Support/Claude/claude_desktop_config.json) and add:
Fully quit Claude Desktop (not just close the window) and reopen. The relay should appear in the tools menu with six tools.
Gotcha: Claude Desktop rewrites claude_desktop_config.json on some session lifecycle events and can silently wipe manual mcpServers additions. If your relay disappears between sessions, re-add the block and keep a backup copy somewhere outside the Claude Desktop config directory so you can paste it back. The Claude.ai custom connector path below avoids this entirely and is preferable if you can use it.
Claude.ai uses OAuth 2.1 with Dynamic Client Registration, which the relay supports.
Relay.<RELAY_URL>/mcp./authorize page.RELAY_API_KEY into the single input and click Authorize.Access tokens last 90 days with automatic refresh, so you should rarely re-authorize. If auth ever fails, remove the connector and re-add.
Common failure modes from real deploys, with the first thing to check for each.
Smoke test fails with 401 Unauthorized. The RELAY_API_KEY in your local environment does not match the secret deployed to the Worker. Re-run npx wrangler secret put RELAY_API_KEY, then re-export the same value in the shell where you run the smoke test. Wrangler does not display secret values after they are set, so if in doubt, rotate to a fresh value on both sides.
Worker returns 5xx on any tool call. Almost always the Supabase service-role key was not set, or was set to the anon key by mistake. Re-run npx wrangler secret put SUPABASE_SERVICE_KEY with the value from Supabase Project Settings -> API -> service_role. Also confirm SUPABASE_URL is the project URL (no trailing /mcp, no path) and RELAY_USER_ID is a valid UUID v4.
Custom domain returns 530. Cloudflare 530 is a DNS resolution failure, usually the CNAME has not propagated yet. Wait a few minutes and retry. If it persists, confirm the hostname in wrangler.toml is on a Cloudflare zone you actually own and that npx wrangler deploy reported the route as attached.
Cursor does not see the relay tools. The relay block is sitting at the top level of .cursor/mcp.json instead of inside the mcpServers object. Cursor silently ignores top-level entries. Move the block inside mcpServers and restart Cursor.
Claude Desktop does not see the relay tools. Two likely causes. First, mcp-remote is missing or npx cannot fetch it on launch (Claude Desktop swallows stderr); run npx -y mcp-remote --help once in a terminal to prime the cache and surface any install errors. Second, Claude Desktop has overwritten claude_desktop_config.json and wiped your mcpServers entry; re-add it from your backup and fully quit and reopen the app.
OAuth flow on Claude.ai loops back to the authorize page. The browser blocked third-party cookies on the Worker domain, or your RELAY_API_KEY was pasted with surrounding whitespace. Try a fresh browser profile, paste the key carefully, and watch the Worker logs (npx wrangler tail) for the actual error.
Once connected, you describe intent. The model picks the right tool. Some examples of sentences that work:
migration-debug, surface code."daily-standup, show me everything Cowork posted this morning."migration-debug."Short, dash-separated, topic-scoped. migration-debug, not april_migration_issues_2026. One thread per topic, not one per day. Threads accumulate; conversations continue across weeks. A thread auto-creates the first time anything posts to it, so there is no ceremony around starting one.
Good: migration-debug, daily-standup, pricing-notes, scratch.
Bad: april-18-bugs, thread-1, general.
Always set surface to chat, cowork, code, or other. Six months from now when you scroll a thread, knowing a message came from a scheduled Cowork task versus a live Chat conversation changes how you weight it. Use session_tag for free-text grouping inside a surface (e.g. one tag per debugging session).
When a topic is done, call relay_archive_thread. Archived threads hide from the default list_threads output but stay queryable via include_archived. Think Slack channels, not Git branches. Archive preserves history; it does not delete.
The relay is a conversation layer between sessions. It is not a log, not a decision record, and not a memory store. Anything you will care about next week belongs in your real system of record (decision log, task tracker, docs, code comments, etc.). The relay is what was said in the moment, not what was decided. If a relay post captures a real decision, write it down somewhere durable before moving on.
Same rule as any chat. API keys, service-role tokens, OAuth secrets, database credentials. Those go in Wrangler secrets or your password manager. They never go in a relay message. The relay database is not a vault. See Security for the full list of what not to post.
This section consolidates the relay's auth model, key rotation procedure, content rules, and threat model.
Static Bearer. Claude Code and Cowork authenticate with Authorization: Bearer <RELAY_API_KEY>. The Worker compares the header to the RELAY_API_KEY secret on every request. There is no browser flow, no token exchange, no refresh. Whoever has the key has full access to every thread under the configured RELAY_USER_ID.
OAuth 2.1 with DCR. Claude.ai custom connectors use OAuth 2.1 with Dynamic Client Registration against /register, /authorize, and /token. The user pastes their RELAY_API_KEY once into the Worker's authorize page; the Worker verifies it and issues an HS256 JWT signed with that same RELAY_API_KEY. Access tokens last 90 days, refresh tokens 365. No server-side session store, no KV, no Durable Objects.
Rotate RELAY_API_KEY with:
Consequences to plan for:
RELAY_API_KEY, so changing the secret breaks every existing signature. Every Claude.ai connector user must remove and re-add the connector and re-authorize with the new key..mcp.json, .cursor/mcp.json, claude_desktop_config.json, and any Cowork task mcp_servers blocks with the new key. Until each is updated, that client returns 401.Rotate when a key is suspected exposed, when a teammate with access leaves, or on a routine schedule if your threat model calls for one.
Threads are persisted in Supabase and are visible to anyone holding the RELAY_API_KEY. Treat the relay as a shared whiteboard, not a vault. Do not post:
Secrets belong in Wrangler secrets or a password manager. The relay database is not a vault.
The relay is single-tenant in v1. It assumes the operator trusts every session that holds the RELAY_API_KEY, because any holder can read and write every thread under the configured RELAY_USER_ID. There is no per-session scoping, no audit trail beyond Worker logs, and no policy layer between the Worker and Supabase. Multi-user or multi-tenant deployments need additional auth layering (per-user keys, scoped tokens, RLS policies keyed off user_id) that is not provided here. The schema already carries user_id columns to make that extension straightforward, but you have to build it.
Three tables, all prefixed relay_. Migration at migrations/001_initial.sql.
relay_threads. One row per named thread per user.relay_messages. One row per posted message. Indexed on (thread_id, created_at desc).relay_read_cursors. One row per (thread_id, reader_tag). Tracks "last time this reader checked."Service-role access only. RLS is enabled with zero policies, and anon and authenticated are revoked. Only the Worker's service-role key can read or write.
This is not an actively maintained community project. PRs are welcome for bugfixes, documentation improvements, and obvious quality-of-life additions. Larger features or refactors will likely be declined to keep the surface area small. Open an issue first if you want to discuss something nontrivial.
MIT. See LICENSE.