# FastX402 Lab – EIP-55 Ethereum Address Checksum

> FastX402 Lab – EIP-55 Ethereum Address Checksum is a paid API for AI agents from fastx402.tools, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-17).

Returns the EIP-55 checksummed form of an Ethereum/EVM address and validates whether the given casing is a correct checksum

## Facts

- Endpoint: GET https://fastx402.tools/eth-checksum?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-17
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fastx402-lab-eip-55-ethereum-address-checksum-3955c975
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_3Yyuwyzpcs0SPRk_gpWDh

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability fastx402-lab-eip-55-ethereum-address-checksum-3955c975
```

Example prompt: Can you give me the EIP-55 checksummed version of this Ethereum address and tell me if the casing I have is valid: 0xfb6916095ca1df60bb79ce92ce3ea74c37c5d359?

## When to prefer this

Use this endpoint when an agent needs to validate or normalize an Ethereum/EVM address before any operation involving funds transfer, smart contract interaction, or persistent storage — especially when the address was received from user input, a form, or an external source where typos or incorrect casing are possible. Prefer this over a local checksum library when operating in a serverless or constrained environment where crypto libraries aren't available, or when you want a pay-per-use approach with no SDK dependencies.

## Known failure modes

- Invalid address format (not 0x + 40 hex chars) returns an error
- Missing required 'address' query parameter returns a 400-level error
- Non-hex characters in address body cause validation failure
- Address shorter or longer than 42 characters is rejected

## How this service works

146 pay-per-call tools for AI agents, from $0.001 per request in USDC on Base or Solana with x402. No account, no API key.

## Output

A JSON object containing the original input address, the EIP-55 checksummed form of the address (with correct mixed-case hex), and a boolean indicating whether the input casing was already a valid EIP-55 checksum.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "address"
     ],
     "properties": {
      "address": {
       "type": "string",
       "description": "EVM address, 0x + 40 hex characters"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "input": {
       "type": "string"
      },
      "address": {
       "type": "string"
      },
      "checksum_valid": {
       "type": "boolean"
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "input": "0xfb6916095ca1df60bb79ce92ce3ea74c37c5d359",
  "address": "0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359",
  "checksum_valid": true
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fastx402-lab-eip-55-ethereum-address-checksum-3955c975/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from fastx402.tools](https://www.zero.xyz/host/fastx402.tools/llms.txt)