Frankfurter API Skill

An Agent Skill that teaches AI agents (Claude Code, Claude.ai, and other skill-compatible agents) how to use the free Frankfurter exchange rate API.

Frankfurter tracks daily reference rates from 84 central banks, covering 201 currencies with history back to 1948 — no API key, no signup, no quotas.

What the skill enables

Once loaded, an agent can reliably:

• Fetch the latest exchange rates (any base currency, filtered quote list)
• Convert amounts between currencies (e.g. 100 USD → TWD)
• Look up historical rates for a specific date
• Pull time series over a date range, optionally grouped by week/month
• Pin rates to a specific central bank (e.g. providers=ECB) for compliance use
• Request CSV or NDJSON output for data pipelines
• Avoid real-world pitfalls (blocked Python-urllib User-Agent, weekend/holiday date rollback, blended-rate drift)

All request/response examples in the skill were verified against the live API.

Repository layout

skills/
└── frankfurter-api/
    ├── SKILL.md                 # Entry point: quick reference, conversion recipes, tips
    └── references/
        ├── endpoints.md         # Full v2 endpoint reference with verified examples
        └── v1-api.md            # Legacy v1 API (only for maintaining old code)

Installation

Claude Code (plugin marketplace — recommended)

This plugin is distributed through the NanookAI/skills marketplace. Inside Claude Code, run:

/plugin marketplace add NanookAI/skills
/plugin install frankfurter-api@nanookai-skills

The skill is then available in every project, and /plugin marketplace update picks up new versions.

Claude Code (per-project)

Copy the skill folder into your project's .claude/skills/ directory:

cp -r skills/frankfurter-api /path/to/your-project/.claude/skills/

Claude Code (personal, all projects)

cp -r skills/frankfurter-api ~/.claude/skills/

Claude.ai / other agents

Package the skill folder (respecting .skillignore) into a .skill bundle, or upload the skills/frankfurter-api/ folder contents wherever your agent platform accepts skills. The skill is self-contained — no scripts, no dependencies.

Try it

After installing, ask your agent things like:

• "What's the latest USD to TWD rate?"
• "Convert 5000 JPY to EUR"
• "Show me the EUR/USD trend for the last 3 months, grouped by week"
• "Get the official ECB reference rate for GBP on 2020-03-16"

About the API

• Public endpoint: https://api.frankfurter.dev (v2)
• Free for commercial use; see each data provider's terms for the underlying data
• Open source and self-hostable via Docker — see frankfurter.dev

License

The skill documentation in this repository is provided as-is. Frankfurter itself is an independent open-source project — see frankfurter.dev for its license and terms.