Beta — Smart contract audit in progress. We recommend keeping wallet balances under $100 USDC.
CardZero

title: Claude Code description: "Use CardZero from Claude Code via the official SKILL.md."

Claude Code reads CLAUDE.md files in your project for instructions. CardZero ships a Claude-Code-specific SKILL snippet that teaches Claude how to use the API.

One-line install

curl -o CLAUDE.md.cardzero \
  https://raw.githubusercontent.com/mrocker/CardZero/main/plugins/claude-code/SKILL.md

Then append to your project's CLAUDE.md:

cat CLAUDE.md.cardzero >> CLAUDE.md && rm CLAUDE.md.cardzero

Set environment variables

Add to your shell profile (~/.zshrc or ~/.bashrc):

export CARDZERO_API_URL="https://api.cardzero.ai/v1"
export CARDZERO_API_KEY="czapi_…"
export CARDZERO_WALLET_ID="wallet_…"

Reload: source ~/.zshrc.

Verify

In Claude Code, try:

> What's my CardZero balance?

Claude should run a curl command to GET /v1/wallets/$CARDZERO_WALLET_ID/balance and report the result.

What the SKILL teaches Claude

  • Wallet lifecycle — when to call POST /wallets, how to handle the claim key, what to tell the Owner.
  • Payment etiquette — confirm amount + recipient before sending.
  • Error handling — what each error code means and how to recover.
  • Spending limits — read the Config Summary block, respect it.
  • A2A jobs — when to use POST /jobs vs POST /payments (escrow vs direct).

The full SKILL is ~340 lines covering 11 endpoints. View on GitHub.

Tips for Claude Code users

  • Don't share CARDZERO_API_KEY with Claude in chat. Set it as an env var so the SKILL.md can reference $CARDZERO_API_KEY without leaking it.
  • Use a v3 wallet if you anticipate hiring other agents (Job escrow). The Quickstart defaults to v3 for this reason.
  • Watch the daily limit. If your agent hits it, payments fail with DAILY_LIMIT_EXCEEDED. The SKILL teaches Claude to suggest the Owner raise it.

Comparison: SKILL.md vs MCP Server

| | SKILL.md (Claude Code) | MCP Server (Claude Desktop, Cursor, VS Code) | | --- | --- | --- | | Transport | Plain markdown + curl | JSON-RPC over stdio | | Setup | One file append + env vars | Config JSON + restart host | | Tools enumerable | No (Claude reads + improvises curl) | Yes (10 explicit tool definitions) | | Where it works | Anywhere with CLAUDE.md support | MCP-protocol clients only |

Use whichever your toolchain supports. They cover the same API; you can mix them on different agents.