How do I use FundFacts API with Claude Code?

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/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 --header "Authorization: Bearer ffk_..."

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.