How do I use FundFacts API with Claude Code?

Start with the MCP server. One command (or the plugin) gives Claude Code seven read-only fund tools on every FundFacts plan, Free included; in the terminal the results come back as text. The MCP server guide has the tool reference and troubleshooting.

Three pieces, each optional

AGENTS.md is the one that matters most. It is a complete, current description of the API written for coding agents: endpoints, the response envelope, every field of data with type and example, the quota rules, error handling, and a reference client in TypeScript and Python. Claude Code reads it at the start of a session. The public edition is at /llms-full.txt; subscribers download a version with their plan limits and key from the dashboard.

bash
# public edition, no key inside
curl -s https://fundfactsapi.com/llms-full.txt -o AGENTS.md

The skill (.claude/skills/fundfacts-api/SKILL.md in the kit) tells Claude Code when to reach for the API and how to structure fund-data code: cache by ISIN until expiresAt, 300-second timeouts on /funds/{isin}, never ship the key to a browser bundle, show dataAsOf.

The MCP server lets Claude Code *look at real data* while it codes: check a field name, test an ISIN, see what a bond fund's payload contains before writing the parser.

bash
claude mcp add --transport http fundfacts https://fundfactsapi.com/api/mcp

Then run /mcp in a session and sign in with your FundFacts account; the connection appears in the dashboard, where you can disconnect it. To use an API key instead, add --header "Authorization: Bearer ffk_..." to the command.

Or install the FundFacts plugin (public repository: github.com/fundfactsapi/fundfacts-plugin), which adds the server together with four skills that tell Claude Code how to read the fund data: /plugin marketplace add fundfactsapi/fundfacts-plugin, then /plugin install fundfacts@fundfacts, then /mcp to sign in.

Prompts that work

• "Using AGENTS.md, build a Next.js page that takes a list of ISINs and shows name, TER, risk indicator and 5-year annualised return in a table, cached in Postgres until expiresAt."
• "Write a Python script that loads isins.csv through POST /funds in batches of 50, retries pending ISINs after 60 seconds, and writes name, category, TER and AUM to a parquet file."
• "Add a Slack bot command /fund <isin> that replies with the top five holdings and the sector split."

The guide to building a fund app with a coding agent walks through a full session.

Rules the agent should follow

The kit spells these out; they are worth knowing because they explain the code Claude Code writes:

1. Read the key from FUNDFACTS_API_KEY; never commit it.
2. Cache by ISIN with expiresAt; stop before X-RateLimit-Remaining hits zero; sleep Retry-After on 429.
3. Timeout of 300 seconds on the single-fund endpoint; a loading state in UIs for cold ISINs.
4. Retry only 502 upstream_error, at most twice; never retry 4xx.
5. Treat 404 fund_not_found as "not a covered fund", not a bug.

Paid plans include an AI companion kit generated from the live field reference: an AGENTS.md with every endpoint, field, rule and a reference client; a Cursor rule; a Claude Code skill; the OpenAPI spec and TypeScript types, with your key baked in or read from an environment variable. Download it from the dashboard; the public edition without a key is at /llms-full.txt.