# Cardex

> Cardex helps people decide which Hong Kong credit card to use by giving their AI assistant structured, sourced facts about rebate rates, caps, and card terms. The assistant compares and answers; Cardex itself never ranks cards or names a best card.

Cardex is a pair: an Agent Skill that teaches an assistant what to check before it answers (caps, registration, exclusions, effective dates), and a public remote MCP server that returns the facts. It is open source under the MIT licence.

Status: pre-alpha. Every figure currently served is illustrative synthetic data, not real issuer terms; responses mark this with `provenance.illustrative: true`.

## Set up

- [Skill](https://cardex.brandonhk.com/skill.md): save as `cardex/SKILL.md` in the assistant's skills directory. Also usable as plain instructions for assistants without skill support.
- MCP endpoint: `POST https://cardex.brandonhk.com/mcp` (streamable HTTP, stateless, no auth, no sign-up).
- MCP client config: `{ "mcpServers": { "cardex": { "url": "https://cardex.brandonhk.com/mcp" } } }`

## What it does not do

- Does not rank cards or recommend a best card.
- Does not take card numbers, store which cards a user holds, or see transactions.
- Does not scrape bank sites at request time; facts are curated and every change is human-approved against the issuer's page.

## FAQ

- **Will Cardex tell me which card is best?** No. Cardex provides facts like rebate rates, caps and terms. Your AI assistant compares them for your spend and the cards you hold, and tells you which conditions it couldn't verify.
- **Do I need to give a card number or log in?** No. Cardex takes no card numbers, stores no list of your cards, and sees no transactions. Which cards you hold stays between you and your assistant.
- **Are the numbers accurate?** Cardex is pre-alpha and every figure today is illustrative, not real issuer terms. Real data goes live card by card after verification, each with a link to the issuer's terms and a last-checked date. Confirm with your issuer before a big spend.
- **Which AI assistants work with it?** Assistants that support skills or MCP can install it directly, such as Claude and Cursor. Any other assistant that can read a URL and send an HTTP request can follow the method described in the skill.
- **How is the data updated?** Data is curated ahead of time; nothing is scraped from bank sites on request. Every change is checked against the issuer's page and approved by a person before it goes live.
- **Do I need to sign up or get an API key?** No. The data connection is public, with no sign-up and no key. The source code is on GitHub under the MIT licence.
- **Is Cardex affiliated with any card issuer?** No. Cardex is an open-source project with no affiliation, partnership, or endorsement from any issuer. Card and issuer names are used only to describe facts; the issuer's own terms are final.

## Pages

- [Home (繁體中文，香港)](https://cardex.brandonhk.com/): landing page in spoken Hong Kong Cantonese
- [Home (English)](https://cardex.brandonhk.com/en): English landing page
- [Source code](https://github.com/brandon-wsc/cardex): Worker, skill, product spec (docs/PRD.md) and decision records (docs/adr/)