# Blockscout Arbitrum Message Claim Data Lookup

> Blockscout Arbitrum Message Claim Data Lookup is a paid API for AI agents from api.blockscout.com, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-12).

Retrieves the calldata and outbox address hash needed to claim a specific Arbitrum cross-chain message by message ID and chain

## Facts

- Endpoint: GET https://api.blockscout.com/%7Bchain_id%7D/api/v2/arbitrum/messages/claim/%7Bmessage_id%7D
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/blockscout-arbitrum-message-claim-data-lookup-627b9fe3
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_PziUoRFoAZ716bg9VgDNZ

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 blockscout-arbitrum-message-claim-data-lookup-627b9fe3
```

Example prompt: Pull the claim calldata and outbox address for Arbitrum message ID 42 on chain 42161 using Blockscout — I need it to execute the withdrawal on L1.

## When to prefer this

Choose this endpoint when you need the exact calldata and outbox address to claim a specific Arbitrum cross-chain message on L1. It is purpose-built for Arbitrum L2-to-L1 message finalization, unlike generic block explorers. Use it over manual RPC calls when you need structured, pre-formatted claim data without constructing raw contract calls yourself.

## Known failure modes

- Invalid or unknown message_id returns an empty or error response
- Invalid chain_id results in a 404 or unsupported chain error
- Message not yet claimable (still in challenge period) may return incomplete data
- Malformed path parameters return a 400 or validation error
- Network timeout if the Blockscout node is temporarily unavailable

## How this service works

Explore crypto activities with Blockscout's multichain search. Find transactions, addresses, tokens, and dapps across top blockchain networks — your go-to explorer for cross-chain blockchain data

## Output

Returns a JSON object containing the raw calldata string needed to execute the claim transaction and the outbox_address_hash (the Arbitrum outbox contract address) associated with the specified message ID on the given chain.

## 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",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "pathParams": {
     "type": "object",
     "properties": {
      "chain_id": {
       "type": "string"
      },
      "message_id": {
       "type": "integer"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "calldata": "string",
  "outbox_address_hash": "string"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/blockscout-arbitrum-message-claim-data-lookup-627b9fe3/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.blockscout.com](https://www.zero.xyz/host/api.blockscout.com/llms.txt)