Official exchange rates in OpenAI Codex: the AllRatesToday Codex plugin
A coding agent that writes your currency logic should not guess the numbers it tests it with. Ask Codex to "add a GBP to EUR conversion and check it against today's rate" and, without a tool, the rate it checks against is whatever was common in its training data. The AllRatesToday Codex plugin gives Codex the published figure instead: the rate an institution printed on a named day, with the institution and the date in the answer.
The plugin is the same package OpenAI approved for the ChatGPT app directory, now installable in Codex as a plugin, and it has its own page on the independent tracker Codex Plugin Stats:
AllRatesToday on Codex Plugin Stats
What the plugin contains
A Codex plugin is a small folder: a manifest, an MCP server configuration and one or more skills. Ours has one skill and one server, and no code of its own runs on your machine.
- The skill tells Codex when to use the tools and how to answer: never quote a rate from memory, multiply the user's amount by the returned rate yourself, always name the institution and the publication date, and say plainly when a pair was derived inside a bank's table rather than printed by it.
- The MCP server is the keyless public profile of our hosted server at
https://allratestoday.com/api/mcp/public, with five read-only tools: an official daily exchange rate for a pair, the supported currencies, the covered institutions, any institution's latest table, and the 16:00 London daily reference rate.
Codex Plugin Stats lists the full package, including the skill text, under "Files and skills", so you can read exactly what Codex is told before you install it.
Installing it
- In Codex, open the plugin catalog and add AllRatesToday, or browse to it from the Codex Plugin Stats page. There is no account to create and no key to paste.
- If you prefer to skip the plugin and wire the server by hand, add it to
~/.codex/config.toml:
[mcp_servers.allratestoday]
url = "https://allratestoday.com/api/mcp/public"Either way, the tools appear in Codex's tool list and the model picks them up when a question is about exchange rates. The manual route gives you the tools without the skill, so you may want to add the "name the institution and the date" rule to your own instructions file.
What you can ask Codex once it is installed
| You ask | What Codex does |
|---|---|
| "Convert 500 GBP to EUR at the official daily rate." | Calls the exchange-rate tool, multiplies, and reports the ECB figure with its date. |
| "Write a test fixture with today's ECB rates for USD, JPY and CHF." | Fetches the ECB table and writes the fixture with the real published values and the rate date in a comment. |
| "Which code do I pass for the Reserve Bank of India?" | Lists the covered institutions and returns the code, with the bank's latest publication date. |
| "Use the Bank of England rate for GBP/USD in this invoice script, not a market quote." | Pulls the BoE table and uses that print, flagged as official, not live. |
| "Give me one reproducible EUR/USD number for 31 October." | Returns the 16:00 London reference rate and repeats that it is a daily snapshot, not a registered benchmark. |
What it deliberately does not do
- No live market quotes. The plugin serves official daily publications, which can lag the market by a day. The answer always carries the day. If your code needs a one-minute mid-market rate, use the API or the full MCP endpoint, not the plugin.
- No dated tables or history. Those need a free API key and live on the full endpoint at
https://allratestoday.com/api/mcp. The public profile is latest-only so it can stay keyless. - No payments, no transfers, no user data. It is a lookup tool. The server receives the currency and bank codes for the question and nothing else, as the privacy policy describes.
Why the two surfaces share one package
OpenAI's plugin format is the same for ChatGPT apps and Codex plugins: one manifest, one MCP configuration, one skills folder. We kept it that way on purpose. The ChatGPT app is for people who want a currency converter in a chat. The Codex plugin is for the same rates inside a coding session, where the common jobs are test data, fixtures, reconciliation scripts and "what does this bank actually publish". Both call the same five tools, so an answer in ChatGPT and an answer in Codex come from the same table on the same day.
Where the numbers come from
The same pipeline that feeds the central bank rates API: each institution's own publication, collected on its own schedule, stored in the direction the publisher quotes it, with a cross-source plausibility check before anything is served. The institutions and their source pages are on the data sources page, and the reference rate has its own page.
Other clients
Claude Code has its own plugin, OpenClaw has a skill, and Cursor, VS Code, Windsurf, Gemini CLI and Claude Desktop connect to the hosted server directly. Setup for each is on the MCP page, and the REST equivalents are in the docs.
Add it to Codex
Install the plugin, then ask for a conversion at the official rate. No account with us, no key.
AllRatesToday on Codex Plugin Stats