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Relay

by adarshp14
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Hybrid

Relay is an open-source runtime that unifies your integrations — OpenAPI, GraphQL, MCP, and Google Discovery — into a single tool catalog. Connect once, use everywhere: from Claude Code and Cursor to custom agents built with the SDK.

Architecture

Related MCP server: Enterprise MCP Gateway and Tool Registry

Quick Start

npm install -g relay
relay web

Opens a local runtime with a web UI at http://127.0.0.1:4788. Add your first source and start using tools.

Use as an MCP Server

Point any MCP-compatible agent at Relay to share your tool catalog, auth, and policies across all of them.

relay mcp

Example mcp.json for Claude Code / Cursor:

{
  "mcpServers": {
    "relay": {
      "command": "relay",
      "args": ["mcp"]
    }
  }
}

SDK

Three entry points — pick the one that fits:

Import

Use case

@relay-sh/sdk

Promise-based. Scripts, quick integrations, non-Effect codebases.

@relay-sh/sdk/core

Effect-native. Full type safety, streaming, composable pipelines.

@relay-sh/sdk/testing

Mocks and utilities for writing tests against your tools.

import { createRelay } from "@relay-sh/sdk";

const relay = await createRelay();

await relay.openapi.addSpec({
  url: "https://petstore3.swagger.io/api/v3/openapi.json",
});

const tools = await relay.tools.list();
console.log(tools);

await relay.close();

Adding Sources

Relay has first-party support for OpenAPI, GraphQL, MCP, and Google Discovery. The plugin system is open to any source type.

Web UI

Open http://127.0.0.1:4788 → Add Source → paste a URL. Relay detects the type, indexes tools, and handles auth.

CLI

relay call relay openapi addSource '{
  "spec": "https://petstore3.swagger.io/api/v3/openapi.json",
  "namespace": "petstore",
  "baseUrl": "https://petstore3.swagger.io/api/v3"
}'

Using Tools

Programmatic

const matches = await tools.discover({ query: "github issues", limit: 5 });

const detail = await tools.describe.tool({
  path: matches.bestPath,
  includeSchemas: true,
});

const issues = await tools.github.issues.list({
  owner: "vercel",
  repo: "next.js",
});

CLI

relay tools search "send email"
relay call github issues create '{"owner":"octocat","repo":"Hello-World","title":"Hi"}'
relay call gmail send '{"to":"alice@example.com","subject":"Hi"}'

If an execution pauses for auth or approval:

relay resume --execution-id exec_123

CLI Reference

relay web                               Start runtime + web UI
relay daemon run | status | stop        Manage background daemon
relay mcp                               Start MCP endpoint
relay call <path...> '{"k":"v"}'        Invoke a tool by path
relay call <path...> --help             Browse namespaces and methods
relay resume --execution-id <id>        Resume paused execution
relay tools search "<query>"            Search tools by intent
relay tools sources                     List sources + tool counts
relay tools describe <path>             Show tool schema

Project Structure

apps/
  cli/            CLI (relay command)
  local/          Local runtime server
  cloud/          Hosted service
  desktop/        Desktop app
  marketing/      relay.sh website

packages/
  core/
    sdk/          Core contracts, plugin wiring, scopes, policies
    execution/    Execution engine
    config/       Configuration and scope management
    storage-*/    Storage adapters
  plugins/
    openapi/      OpenAPI plugin
    graphql/      GraphQL plugin
    mcp/          MCP plugin
    google-*/     Google Discovery plugin
  kernel/
    quickjs/      QuickJS sandboxed runtime
    deno/         Deno subprocess runtime
    ir/           IR compiler
  react/          React UI components
  hosts/
    mcp/          MCP host surface

Development

bun install
bun run dev

Dev server starts at http://127.0.0.1:4788.

bun run test          # run tests
bun run lint          # oxlint
bun run typecheck     # type checking
bun run format        # oxfmt

See CONTRIBUTING.md for full setup instructions.

License

MIT

This server cannot be deployed

One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

Maintenance

ActivityInactive
ResponsivenessNo issues

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