Connect Claude, Cursor, ChatGPT and other clients

Every client connects to the same gateway URL over Streamable HTTP. Most sign in with OAuth: each person signs in to Fastn Connect once and calls run as them. Clients that cannot sign in take an access key, which an admin creates from Connect a client on Home or the Agents page. The examples use https://mcp.fastn.dev/your-company; Home shows your own URL.

Claude

On Home, Connect a client > Claude has an Add to Claude button that opens the client with your URL filled in.

• Click Add to Claude. claude.ai opens Add custom connector with the name and URL filled in. By hand: Customize > Connectors > Add > Add custom connector, then paste the URL.
• Leave the detected sign-in settings as they are and click Add, then Connect.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• In a chat, click + > Connectors and check fastn is on. The Claude desktop app shares these connectors; only if you manage Desktop through its config file, use the mcp-remote entry below.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

claude_desktop_config.json (only if you manage Desktop by file):

{
  "mcpServers": {
    "fastn": {
      "command": "npx",
      "args": [
        "-y",
        "mcp-remote",
        "https://mcp.fastn.dev/your-company"
      ]
    }
  }
}

Claude Code

Sign in (OAuth):

• Run the add command. Add --scope user to use fastn in every project.
• Run claude mcp login fastn, or type /mcp in a session and pick Authenticate.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

claude mcp add --transport http fastn https://mcp.fastn.dev/your-company
claude mcp login fastn

Access key:

• Run the add command with the key as a header.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

claude mcp add --transport http fastn https://mcp.fastn.dev/your-company \
  --header "Authorization: Bearer ucl_<access-key>"

ChatGPT

• In ChatGPT, open Plugins in the sidebar, click Add and choose Add custom MCP server.
• Enter the name fastn and the server URL, leave Authentication on OAuth, tick I understand and want to continue, and click Create as a plugin.
• Click Connect fastn.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• Start a new chat and name it: Using the fastn plugin, list my tools.

Cursor

Sign in (OAuth):

On Home, Connect a client > Cursor has an Add to Cursor button that opens the client with your URL filled in.

• Click Add to Cursor and allow the browser to open Cursor. Or add the entry to ~/.cursor/mcp.json (every project) or .cursor/mcp.json (one repository).
• Click Install, then Authenticate on fastn under Customize > MCPs.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

~/.cursor/mcp.json:

{
  "mcpServers": {
    "fastn": {
      "url": "https://mcp.fastn.dev/your-company"
    }
  }
}

Access key:

• Add the entry to ~/.cursor/mcp.json.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

~/.cursor/mcp.json:

{
  "mcpServers": {
    "fastn": {
      "url": "https://mcp.fastn.dev/your-company",
      "headers": {
        "Authorization": "Bearer ucl_<access-key>"
      }
    }
  }
}

VS Code

Sign in (OAuth):

On Home, Connect a client > VS Code has an Install in VS Code button that opens the client with your URL filled in.

• Click Install in VS Code, then Install. Or add the entry to .vscode/mcp.json: the key is servers, not mcpServers.
• Run MCP: List Servers, pick fastn and choose Start Server. Allow it to authenticate.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• Open Chat in Agent mode and check fastn is ticked under the tools icon.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

.vscode/mcp.json:

{
  "servers": {
    "fastn": {
      "type": "http",
      "url": "https://mcp.fastn.dev/your-company"
    }
  }
}

Access key:

• Add the entry to .vscode/mcp.json, then MCP: List Servers > fastn > Start Server.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

.vscode/mcp.json:

{
  "servers": {
    "fastn": {
      "type": "http",
      "url": "https://mcp.fastn.dev/your-company",
      "headers": {
        "Authorization": "Bearer ucl_<access-key>"
      }
    }
  }
}

Codex

Sign in (OAuth):

• Run the add command. Codex detects OAuth and opens the sign-in straight away; the CLI and the IDE extension share ~/.codex/config.toml.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• To sign in again later, run codex mcp login fastn.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

codex mcp add fastn --url https://mcp.fastn.dev/your-company

~/.codex/config.toml:

[mcp_servers.fastn]
url = "https://mcp.fastn.dev/your-company"

Access key:

• Export the key, then point Codex at the variable. Codex reads the key from the environment, never from the file.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

export FASTN_KEY="ucl_<access-key>"
codex mcp add fastn --url https://mcp.fastn.dev/your-company --bearer-token-env-var FASTN_KEY

~/.codex/config.toml:

[mcp_servers.fastn]
url = "https://mcp.fastn.dev/your-company"
bearer_token_env_var = "FASTN_KEY"

Antigravity

• Add fastn to ~/.gemini/config/mcp_config.json. The key must be serverUrl: an entry with url or httpUrl loads no tools.
• Open Customizations > MCP Servers, refresh, and click Authenticate on fastn.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• Copy the code Google shows, paste it into Enter authorization code in Antigravity and click Submit.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

~/.gemini/config/mcp_config.json:

{
  "mcpServers": {
    "fastn": {
      "serverUrl": "https://mcp.fastn.dev/your-company"
    }
  }
}

Devin

• In Devin Desktop (formerly Windsurf), open Customize > MCPs, click + and choose New MCP. From the Devin CLI, run the two commands below instead.
• Name it fastn, set Transport type to HTTP, paste the server URL, set Authentication to OAuth and click Add.
• Click Connect MCP on fastn's row.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

Devin CLI:

devin mcp add -s user fastn https://mcp.fastn.dev/your-company
devin mcp login fastn

Cline

Sign in (OAuth):

• In Cline, open the MCP tab and click Add Remote Server. Paste the URL and keep Streamable HTTP. Or click Edit Configuration and add the entry; type must be streamableHttp, exactly.
• Click Authenticate on fastn's row.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• Pick a model that accepts more than 128 tools if your workspace exposes that many.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

cline_mcp_settings.json:

{
  "mcpServers": {
    "fastn": {
      "type": "streamableHttp",
      "url": "https://mcp.fastn.dev/your-company"
    }
  }
}

Access key:

• Click Edit Configuration in Cline's MCP tab and add the entry.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

cline_mcp_settings.json:

{
  "mcpServers": {
    "fastn": {
      "type": "streamableHttp",
      "url": "https://mcp.fastn.dev/your-company",
      "headers": {
        "Authorization": "Bearer ucl_<access-key>"
      }
    }
  }
}

Lovable

Sign in (OAuth):

• In Lovable, open Connectors, click Add custom and choose MCP server.
• Name it fastn, paste the server URL, leave Authentication on OAuth and click Add & authorize. Allow the popup if the browser blocks it.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

Access key:

• In Lovable, open Connectors, click Add custom and choose MCP server.
• Name it fastn, paste the server URL, set Authentication to Bearer token, paste the key and click Add.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

Bearer token:

ucl_<access-key>

Bolt

• In bolt.new, click + in the chat box, then Connectors > Manage connectors > Custom MCP server.
• Name it fastn, paste the URL, keep HTTP, set Authentication to MCP OAuth and click Add MCP server.
• Bolt does not say which URL it is connecting to, so Fastn Connect asks which apps Bolt may reach. Tick the ones it should use and authorize.
• In the chat box, click + > Connectors and switch fastn on for the project.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

Zed

Sign in (OAuth):

• Add the entry to Zed's settings.json, or use Settings > AI > MCP Servers > Add Server > Add Remote Server.
• With no Authorization header, Zed prompts you to sign in.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• The dot next to fastn turns green.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

settings.json:

{
  "context_servers": {
    "fastn": {
      "url": "https://mcp.fastn.dev/your-company"
    }
  }
}

Access key:

• Add the entry to Zed's settings.json.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

settings.json:

{
  "context_servers": {
    "fastn": {
      "url": "https://mcp.fastn.dev/your-company",
      "headers": {
        "Authorization": "Bearer ucl_<access-key>"
      }
    }
  }
}

Any other client

Sign in (OAuth):

• Add the URL as a remote server over Streamable HTTP.
• The first unauthenticated request gets a 401 whose WWW-Authenticate header points at the OAuth metadata. A client that implements MCP authorization registers itself (dynamic registration or a client ID metadata document) and opens the sign-in.
• Your browser opens Fastn Connect. Sign in if asked and approve the connection.
• Ask the client "list my tools". It answers with the tools your workspace exposes.

Access key:

• Send the key as a bearer token on every request. Each request is a JSON-RPC POST, and Accept must allow both JSON and an event stream.

curl https://mcp.fastn.dev/your-company \
  -H "Authorization: Bearer ucl_<access-key>" \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Headless agents (LangChain, OpenAI, TypeScript)

For agents serving many end users, create one client per user and bind the org + end-user headers at connect time. The same agent key serves every tenant; per-user connectors act as the X-User-Id you pass.

from langchain_mcp_adapters.client import MultiServerMCPClient

client = MultiServerMCPClient({
    "fastn": {
        "transport": "streamable_http",
        "url": "https://mcp.fastn.dev/your-company",
        "headers": {
            "Authorization": "Bearer ucl_<agent-key>",
            "X-Org-Id": "acme",
            "X-User-Id": "user@acme.com",
        },
    }
})