Frankfurter is an open-source API that provides daily currency exchange rates collected from institutional sources. Developers use it to retrieve currency data, convert amounts, or run their own instance with Docker. The catalogue entries are add-ons for working with the API.
Borrowing it
Nothing to install: this file belongs to lineofflight/frankfurter. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/lineofflight/frankfurter/main/.agents/skills/implementing-providers/SKILL.mdgit clone --depth 1 https://github.com/lineofflight/frankfurterWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/lineofflight/frankfurter/implementing-providers)<a href="https://agentmods.dev/skills/lineofflight/frankfurter/implementing-providers"><img src="https://agentmods.dev/badge/skills/lineofflight/frankfurter/implementing-providers/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/lineofflight/frankfurter/implementing-providers"><img src="https://agentmods.dev/badge/skills/lineofflight/frankfurter/implementing-providers.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00057 | $0.04348 |
| Opus 5.5 | $0.00023 | $0.01739 |
| Sonnet 5.5 | $0.00011 | $0.00870 |
| Haiku 4.5 | $0.00006 | $0.00435 |
Grade A, and why
implementing-providers scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
- `fetch(after: nil, upto: nil)` — fetches from the source API, returns an array of records How it starts
The opening of the file, as written. The whole thing — 191 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Adding a New Provider
Checklist for adding a new exchange rate data provider. Each step references an existing provider as a pattern to follow.
Before You Start
- Identify the API endpoint and authentication requirements
- Verify the API is accessible — make a test request and confirm you get a 200 response with valid data. If the API returns 403, times out, or is otherwise inaccessible, stop here. Do not proceed with a hand-crafted cassette or fake data.
- Read the API docs — understand pagination, date filtering, and rate limiting. Some APIs require specific params for date ranges (e.g., HKMA needs
choose=end_of_dayforfrom/toto work). Getting this right avoids downloading the entire dataset on every request. - Confirm the base currency and available quote currencies
- Check the publish schedule (timezone, frequency, days of week)
- Determine the earliest available date for historical data (goes in
coverage_startin the seed file)
Go/no-go: does the provider backfill meaningfully?
Before writing code, confirm the provider has a usable historical archive. If not, don't implement it — forward-only providers accumulate permanent gaps each year and the maintenance cost outweighs the value.
Stop and skip the provider if either of these is true:
- Live page only, no historical endpoint. Every year (or whenever the scheduler misses a window) leaves a permanent hole. Even a fresh deploy is forward-only from day one.
- Archive exists but lags badly. An archive that's months behind the live page means anything between the last archive entry and "now" is permanently lost if we don't catch it live.
If the provider has a real archive (downloadable history reaching back years, not just the current snapshot), proceed. Note coverage_start from the earliest archive date and continue with the checklist.
Licence: when terms block a provider
Find the source's terms or legal page and record it as terms_url (null if there is none). Read it. A licence blocks a provider only when it explicitly forbids what Frankfurter does: free redistribution of published official rates, with attribution, by a non-commercial open-source service.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago Changed ff012217c522
- 1mo ago Changed · -2 lines 05a68d2727d4
- 1mo ago Changed · +2 lines e3d4d238bf77
- 1mo ago Changed 8c04c13cdfef
- 1mo ago Changed · +44 lines 0e10ccdebc39
- 2mo ago First seen · 147 lines · 57 tokens per session scan A 787e31ad15f8
implementing-providers is a skill published in the GitHub repository lineofflight/frankfurter (2,069 stars, last pushed 2d ago), licensed MIT. It adds 57 tokens to every session and 4,348 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
implementing-providers compared with skills from other repositories
| Mod | Type | Stars | Last push | Licence | Scan | Tokens | Works with |
|---|---|---|---|---|---|---|---|
| implementing-providerslineofflight/frankfurter | Skill | 2.1k | 2d ago | MIT | A | 57 | Claude Code, Codex |
| gmgn-contract-ddGMGNAI/gmgn-skills | Skill | 645 | 8d ago | MIT | A | 367 | Claude Code |
| gmgn-marketGMGNAI/gmgn-skills | Skill | 645 | 8d ago | MIT | A | 153 | Claude Code |
| gmgn-heat-rankGMGNAI/gmgn-skills | Skill | 645 | 8d ago | MIT | A | 728 | Claude Code |
| gmgn-swapGMGNAI/gmgn-skills | Skill | 645 | 8d ago | MIT | A | 399 | Claude Code |
| gmgn-wallet-analysisGMGNAI/gmgn-skills | Skill | 645 | 8d ago | MIT | A | 290 | Claude Code |
| gmgn-wallet-scoreGMGNAI/gmgn-skills | Skill | 645 | 8d ago | MIT | A | 232 | Claude Code |