# SendCheck — EVM address verification (x402)

Checks an EVM address before your agent signs a payment. The free pre-check catches typos and bad casing; paid tiers cover chain data.

- MCP server · `type=mcp` · Claude Code, Codex, Cursor, GitHub Copilot, Windsurf (Devin Desktop), Cline, Zed, Gemini CLI
- Author: pennyforgeorg
- License: MIT · policy=link-only · description only; the file stays with the author
- Source: https://github.com/pennyforgeorg/sendcheck-verify
- Updated: 2026-09-10
- HTML: https://affpapa.org/en/nevibecode/mcp/sendcheck-evm-address-verification-x402

## What it does

Point the server at `https://api.pennyforge.org/mcp` and it exposes SendCheck's address checks to your agent. The free `/validate` endpoint answers one question: is this a well-formed EVM address with a correct EIP-55 checksum? That alone stops the costly mistake, since a dropped digit or a flipped character in a settlement address sends USDC somewhere it cannot come back from.

Paid routes cost $0.01 for one chain or $0.05 for all five, settled in USDC on Base through x402. No account, no API key. Version v0.2.0 adds signed service cards: the worker signs its payTo address and per-route max price with a stable ES256 key on every deploy, and a client that pinned that key once can confirm the payTo in a 402 challenge cryptographically. `verifyChallenge` compares the challenge against the signed block and reports reasons such as `challenge_payto_mismatch` or `price_exceeded`.

The client library needs Node 18+ for global `fetch` and pulls in no dependencies. Installing from the GitHub npm registry wants a valid GitHub token even for public reads, so `//npm.pkg.github.com/:_authToken=<your GH token>` has to sit in your `.npmrc` or the install fails. First contact is still trust-on-first-use: the signature gives key continuity to clients that already pinned the key, not proof of authenticity on a first visit.

## Requirements
- Remote server: `https://api.pennyforge.org/mcp`

## Install

### Claude Code (native platform)

**Platform CLI: remote server**
```bash
claude mcp add --transport http sendcheck https://api.pennyforge.org/mcp
```

### Codex

**Platform CLI: remote server**
```bash
codex mcp add sendcheck-evm-address-verification-x402 --url https://api.pennyforge.org/mcp
```

### Cursor

**Config file**
File `.cursor/mcp.json`:
```json
{
    "mcpServers": {
        "sendcheck-evm-address-verification-x402": {
            "url": "https://api.pennyforge.org/mcp"
        }
    }
}
```

### GitHub Copilot

**Config file**
File `.vscode/mcp.json`:
```json
{
    "servers": {
        "sendcheck-evm-address-verification-x402": {
            "type": "http",
            "url": "https://api.pennyforge.org/mcp"
        }
    }
}
```

### Gemini CLI

**Platform CLI: remote server**
```bash
gemini mcp add -t http sendcheck-evm-address-verification-x402 https://api.pennyforge.org/mcp
```

## When to use it
- catch a mistyped settlement address before signing a payment
- confirm an address matches its EIP-55 checksum
- check that the payTo in a 402 challenge matches the signed service card
- flag a challenge priced above the signed maxPrice
- notice when a service rotates its signing key

## Example prompts
- Verify `0x9504A5939AB5be2B2B1F8beA7D7ebeCcd96c485D` before I pay
- Compare the payTo in this 402 challenge against the signed service card
- Pin the public key for `https://api.pennyforge.org` and tell me if it rotated

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