Relay

@relaygpu/mcp

Relay's MCP server. Your agent can find a Relay model, read its input schema, run it, poll long tasks, upload files, run workflows and search the Relay docs, all from Claude Code, Cursor, VS Code or Claude Desktop. It is built on @relaygpu/client. The tools are generic and take the model as a string, so a model added to Relay works without a new release.

Connect to the hosted server, or run it locally:

The server never stores your key: the hosted one reads it from each request and uses it for that request only, the local one reads it from its environment.

Install

Claude Code, Codex, Cursor and VS Code connect to the hosted server: no Node, no npx. Claude Desktop accepts remote servers only through OAuth, which v0 does not offer yet, so it uses the local server through a one-click bundle. Every client can also run the local server; see Local server.

Claude Code

Terminal, in the CLI or the VS Code / JetBrains extension alike:

claude mcp add --transport http --scope user relay https://mcp.relaygpu.com/mcp --header "X-API-Key: relay_sk_..."

--scope user makes it available in every project; without it the server exists only in the directory you ran the command in. Check it with /mcp in a new session. If the terminal answers command not found: claude, the extension is installed but the CLI is not: install it with curl -fsSL https://claude.ai/install.sh | bash (or npm install -g @anthropic-ai/claude-code).

Codex

Codex sends the key as a Bearer token from an environment variable, so the key stays out of config.toml. Set RELAY_API_KEY in your shell profile, then:

codex mcp add relay --url https://mcp.relaygpu.com/mcp --bearer-token-env-var RELAY_API_KEY

Cursor

The button installs the entry below with a placeholder key; replace relay_sk_... in Cursor's MCP settings afterwards. By hand: ~/.cursor/mcp.json (all projects) or .cursor/mcp.json (one project).

{
  "mcpServers": {
    "relay": {
      "url": "https://mcp.relaygpu.com/mcp",
      "headers": { "X-API-Key": "relay_sk_..." }
    }
  }
}

VS Code (Copilot agent mode)

This installs the server for VS Code's own agent (Copilot Chat). Using Claude Code inside VS Code? Use the Claude Code command instead: the Claude Code extension does not read VS Code's MCP config.

VS Code asks for the key once and keeps it in its secret storage. By hand, in .vscode/mcp.json (one workspace) or with MCP: Open User Configuration (every workspace):

{
  "inputs": [{ "type": "promptString", "id": "relay-key", "description": "Relay API key (relay_sk_...)", "password": true }],
  "servers": {
    "relay": {
      "type": "http",
      "url": "https://mcp.relaygpu.com/mcp",
      "headers": { "X-API-Key": "${input:relay-key}" }
    }
  }
}

Claude Desktop

1. Download relay.mcpb.
2. Double-click it. Claude Desktop opens an install dialog: click Install.
3. The extension installs switched off. Open Settings → Extensions → Relay → Configure.
4. Paste your Relay key and click Save. The key stays in Claude Desktop's secure storage.
5. Switch Relay on.

The bundle runs on Claude Desktop's built-in Node, so nothing else needs to be installed. get_credits and get_usage read the account, so they take a dashboard JWT or a custom-tier superkey, never a plain key; every other tool works with a plain key.

By hand instead: Settings → Developer → Edit Config opens claude_desktop_config.json in your default editor. Add the block below at the top level, save, then quit Claude Desktop (⌘Q) and reopen it:

{
  "mcpServers": {
    "relay": {
      "command": "npx",
      "args": ["-y", "@relaygpu/mcp"],
      "env": { "RELAY_API_KEY": "relay_sk_..." }
    }
  }
}

Local server (stdio)

Any client can run the server on your machine instead; it needs Node 20 or newer on the PATH the client sees (see Troubleshooting).

claude mcp add relay --scope user --env RELAY_API_KEY=relay_sk_... -- npx -y @relaygpu/mcp
codex mcp add relay --env RELAY_API_KEY=relay_sk_... -- npx -y @relaygpu/mcp

Cursor (~/.cursor/mcp.json) and VS Code take the same command / args / env entry as the Claude Desktop block above; VS Code adds "type": "stdio" and lists it under "servers".

Ready-to-copy files are in examples/.

Troubleshooting

• "Server disconnected", "spawn npx ENOENT" or "Executable not found: npx" (Claude Desktop, Cursor). Apps opened from the Dock or Start menu do not load your shell profile, so a Node installed with nvm, Volta or Homebrew is not on their PATH. Use the Claude Desktop bundle, or put the full path in "command": run which npx in a terminal and paste the result (for example /Users/you/.nvm/versions/node/v22.22.0/bin/npx).
• TypeError: Relay: no global fetch: the client started Node 16 or older. Install Node 20 or newer, or point "command" at a newer npx.
• Windows: if the client cannot start npx, use "command": "cmd" with "args": ["/c", "npx", "-y", "@relaygpu/mcp"].
• The first start takes a few seconds: npx downloads the package once (about 5 s); later starts take about 1 s.

Tools

Tools marked keyless work without a credential on the local server. The others are billed or account tools and need one. A hosted server with OAuth on (see Self-hosting) takes no request without a credential, keyless tools included.

Local files

The hosted server cannot read files on your computer. How a local file reaches a model, per client:

Image editors: search_models({tag: "image-to-image"}) lists every image model that takes an input image, each with accepts: ["image"].

Notes

• Auth. On the local server, and on a hosted server without OAuth, tools/list and the keyless tools answer without a credential. A hosted server with OAuth on answers every /mcp request without a credential with 401 and WWW-Authenticate: Bearer resource_metadata="…", scope="relay", which is how clients start the "Connect Relay" sign-in; X-API-Key and Authorization: Bearer <relay key or dashboard JWT> keep working there. A billed tool called without one returns a MISSING_CREDENTIALS tool error that names what to set: the X-API-Key header (hosted) or RELAY_API_KEY (stdio). Errors from Relay come back as tool errors that include the error class, code, requestId and the server's detail. Your key never appears in a tool result or a log line.
• Long tasks. run_model waits up to 45 s (wait_seconds, 0–45). If the task is still running after that, it returns the task_id and the line "Do not resubmit: call check_task with this task_id". Every submit carries an Idempotency-Key, so a retry does not bill twice. Pass your own idempotency_key if your agent might send the same submit again. Since 0.1.7 every model whose input schema takes async (image, video, audio) is submitted as a task, so a long image run returns a task_id, never a 524; chat models still answer inline.
• Expiry. Each result link comes with its expiry: "expires 1 h after completion unless store_output was set". To keep results longer, pass store_output with a media_storage SKU from get_pricing (for example relay7d). That SKU adds a per-file fee.
• Image links. The image routes that answer base64 (Gemini, gpt-image, FLUX-2-pro) also answer Relay's own links (urls); the server returns those links in place of the base64, for 1 h or the store_output lifetime. A result that carries base64 without a Relay link is uploaded through /v2/files (at the store_output retention, else relay1h, free within the daily quota) and comes back as a URL and a file_id. Image content blocks are opt-in: pass inline_images: true, which applies to images of 1 MB or less.
• Uploads. On stdio, upload_file streams a local path of up to 100 MB. The hosted server cannot read your disk: use slot: true (see Local files), base64 (up to 4 MB) or a public url. Retention defaults to relay1h.

Self-hosting

docker build -t relaygpu-mcp .
docker run -p 2300:2300 -e PORT=2300 -e RELAY_BASE_URL=https://relaygpu.com relaygpu-mcp

The server listens on PORT (default 2300) and calls Relay at RELAY_BASE_URL. Endpoints:

• POST /mcp: Streamable HTTP, stateless.
• GET /healthz: returns {status, version}.
• GET /metrics: Prometheus text with mcp_tool_calls_total{tool,outcome} and mcp_tool_seconds{tool}.
• GET /.well-known/mcp/server-card.json: the server and its tools.
• GET /.well-known/oauth-protected-resource (and …/mcp): the RFC 9728 protected-resource metadata, only with OAuth on.

OAuth ("Connect Relay")

OAuth is on when both OAUTH_ISSUER and MCP_RESOURCE_URL are set; with either unset the server behaves as above (no metadata route, keyless tools answer without a credential). All three variables belong to the MCP app and are read once at start:

A Bearer value that is a JWT issued by OAUTH_ISSUER is an access token: the server verifies it (ES256 against the issuer's JWKS, aud, exp with 60 s skew), exchanges it at Relay for a 5-minute Relay credential and keeps that credential in memory per token hash until 30 s before it expires. A bad, expired or revoked token gets 401 with WWW-Authenticate: Bearer error="invalid_token", …; an authorization server that cannot be reached gets 503. Tokens, credentials and the secret are never logged.

Logs are JSON lines on stderr, WARNING and above by default (LOG_LEVEL). Without Docker, run npm ci && npm run build && node dist/http.js.

License

MIT