MCP access - Terrapin

The Terrapin API is available as a Model Context Protocol (MCP) server. Once connected, an AI assistant can call the API endpoints as tools, apart from the REST-only ones, without you writing any integration code. MCP server URL: https://terrapinfinance.com/mcp

In Claude and Claude Code, connect through the Terrapin connector in Claude’s directory, as described in Claude.

What the tools cover

Tools	Data
`securities_*`	Corporate, government, certificate of deposit and US agency bonds: search, reference data, latest and historical prices, and cash flows.
`muni_*`	US municipal bonds: search, issuer search, reference data, documents, latest and historical prices, price to yield, cash flows, and the bonds in a series.
`muni_stats_*`	US municipal market statistics: outstanding, issuance, trade activity, and top issuers.
`government_yield_curve`, `inflation_factors`	Government yield curves for the US, the UK and Germany, and inflation factors.
`convert_to_isin`, `download_document`	CUSIPs to ISINs, and the documents `muni_documents` lists. Over MCP, `download_document` returns a short-lived link to the file rather than the file itself, for an assistant with a terminal or code execution to fetch and convert, for example with `pdftotext`.

Every tool is read-only, and takes the parameters of the API endpoint of the same name.

REST-only endpoints

These endpoints aren’t MCP tools. Call them over HTTP with an API key:

Endpoint	Why
Bulk Pricing (`muni_pricing_daily_history`)	A day of trades runs to tens of megabytes, far more than an assistant can read in one tool result.

Example prompts

Find ten California general obligation bonds issued since 2024 that mature after 2040.
What’s the latest price and yield of US Treasury CUSIP 912810TM0?
Which ten Texas municipal issuers issued the most par value in 2025?
Compare the US Treasury par yield curve on 31 December 2025 with 30 June 2026.

Access and quotas

You need a Terrapin account in an organization whose plan includes API access, such as one of the tiers. New accounts start without it: subscribe in the app, or write to team@terrapinfinance.com. Connecting Claude or ChatGPT creates an API key for the organization you approve, which it sends with every request. Every tool call is an API request, and counts against your organization’s rate limits and quotas like any other.

Claude custom connector (deprecated)

A custom connector holding your API key is deprecated and will stop working. To switch to the Terrapin connector, first remove the custom connector in Claude’s Customize → Connectors, so you don’t end up with two Terrapin connections, then delete the API key you pasted into it under API Keys in the app, since it stays valid until you do.

ChatGPT

ChatGPT connects to remote MCP servers as custom connectors (also called Plugins). You need Developer Mode enabled, which is available on Plus, Business, Enterprise, and Edu plans.

Add a plugin

In ChatGPT, open Settings → Plugins → Add → Add custom MCP server

Fill in the plugin details

Name: Terrapin
Connection URL: https://terrapinfinance.com/mcp

Add your API key

Expand Advanced OAuth settings and paste your Terrapin API key into the OAuth Client Secret field. The OAuth Client ID field accepts any non-empty string, for example Terrapin.

Click Create as plugin. When ChatGPT redirects you to authorize the connection, sign in to your Terrapin account. ChatGPT then calls tools/list and shows the available Terrapin tools. Enable the plugin in a new chat via the tool picker.

Other clients

Other clients send an API key directly, as Authorization: Bearer <API key>.

Cursor

Add the server to ~/.cursor/mcp.json, or to .cursor/mcp.json in a project, and set TERRAPIN_API_KEY in your environment:

mcp.json

{
  "mcpServers": {
    "terrapin": {
      "url": "https://terrapinfinance.com/mcp",
      "headers": {
        "Authorization": "Bearer ${env:TERRAPIN_API_KEY}"
      }
    }
  }
}

Clients that only run local servers

mcp-remote runs locally and relays to Terrapin. It needs Node.js:

{
  "mcpServers": {
    "terrapin": {
      "command": "npx",
      "args": [
        "-y",
        "mcp-remote",
        "https://terrapinfinance.com/mcp",
        "--header",
        "Authorization:${AUTH_HEADER}"
      ],
      "env": {
        "AUTH_HEADER": "Bearer YOUR_API_KEY"
      }
    }
  }
}

Disconnect

Disconnecting in Claude or ChatGPT only makes it forget the connection’s API key, which keeps working. To revoke the key, open API Keys in the app with the organization you approved selected, expand the key whose Created by is you and whose Issued to is the client’s, and delete it:

Client	Issued to
Claude, and Claude Code signed in with your Claude account	`https://claude.ai/oauth/mcp-oauth-client-metadata`
Claude Code, with a server added by `claude mcp add`	`https://claude.ai/oauth/claude-code-client-metadata`
ChatGPT and Codex	`https://chatgpt.com/oauth/client.json`

The key stops working at once, and the client has to sign in again to use Terrapin.

Troubleshooting

Terrapin says your plan doesn’t include API access

The approval page says so when none of your organizations’ plans include API access, and every tool returns HTTP 403 with “does not have permission for API access” when the plan has lapsed since you connected. Subscribe in the app, or write to team@terrapinfinance.com. An existing connection works again as soon as the plan includes API access. If only some tools return 403 with “You do not have permission to access this resource”, your plan doesn’t include that dataset.

Quota or rate limit reached

HTTP 402, “You have run out of your granted quota”: your organization has used its monthly ISIN or document download quota. It resets in the next billing month, or sooner if you upgrade.
HTTP 429, “Too Many Requests”: you’ve hit the per-minute rate limit. Wait a minute and ask the assistant to try again.

Rate limits & quotas has the details.

The result is over the server’s limit

A tool result over 50,000 bytes comes back as an error that tells the assistant how to narrow the call, and it usually retries by itself. If it doesn’t, ask for fewer bonds or a shorter date range. Terrapin no longer accepts the connection’s API key: someone deleted it under API Keys, or you left the organization. Connect again, then sign in and approve.

Calls or document links fail in a sandbox or behind a proxy

If your assistant runs with a domain allowlist, or your network goes through a proxy, allow terrapinfinance.com as described in Network access. Connectors you add in Claude or ChatGPT call Terrapin from Anthropic’s and OpenAI’s servers, so for them it matters only for fetching the links download_document returns.

Support

Write to team@terrapinfinance.com or use the support form, about MCP access, your account or a security concern. Our privacy notice covers the data we keep.

​What the tools cover

​REST-only endpoints

​Example prompts

​Access and quotas

​Claude custom connector (deprecated)

​ChatGPT

​Other clients

​Cursor

​Clients that only run local servers

​Disconnect

​Troubleshooting

​Terrapin says your plan doesn’t include API access

​Quota or rate limit reached

​The result is over the server’s limit

​Claude or ChatGPT asks you to sign in to Terrapin again

​Calls or document links fail in a sandbox or behind a proxy

​Support

What the tools cover

REST-only endpoints

Example prompts

Access and quotas

Claude custom connector (deprecated)

ChatGPT

Other clients

Cursor

Clients that only run local servers

Disconnect

Troubleshooting

Terrapin says your plan doesn’t include API access

Quota or rate limit reached

The result is over the server’s limit

Claude or ChatGPT asks you to sign in to Terrapin again

Calls or document links fail in a sandbox or behind a proxy

Support