# Ethereum Pending Block (Mempool) Fetcher

> Ethereum Pending Block (Mempool) Fetcher is a paid API for AI agents from skills.onesource.io, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-15).

Returns the pending Ethereum block containing mempool transactions not yet mined, using eth_getBlockByNumber('pending'), across multiple EVM-compatible networks

## Facts

- Endpoint: GET https://skills.onesource.io/api/chain/pending
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/skills-onesource-io-f2b6b131
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_d8YqHBwL5cO9TPJ1qSOjS

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 skills-onesource-io-f2b6b131
```

Example prompt: What transactions are currently sitting in the Ethereum mempool waiting to be mined — can you pull the pending block right now?

## When to prefer this

Use this endpoint when you need a real-time snapshot of unconfirmed Ethereum (or EVM-compatible) transactions before they are mined — ideal for MEV research, front-running detection, gas price analysis, or monitoring specific pending transactions. Prefer this over block-by-number endpoints when you specifically need the unmined mempool state rather than confirmed blocks.

## Known failure modes

- Unsupported network value returns validation error
- Network RPC unavailability causes timeout or 5xx error
- Pending block may be empty if mempool is quiet
- Response truncated for very large mempools
- Payment failure returns 402 if USDC balance insufficient

## How this service works

Fetches pending chain data for monitoring in-flight blockchain activity.

## Output

Returns the full pending block object including an array of unconfirmed mempool transactions (with their hashes, from/to addresses, value, gas, data, etc.) and block header fields — response can be very large (100k+ bytes) since it may contain hundreds of pending transactions.

## Example request

```json
{
 "network": "sepolia"
}
```

## 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"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "network": {
       "enum": [
        "ethereum",
        "sepolia",
        "robinhood"
       ],
       "type": "string",
       "default": "ethereum"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "required": [
      "data",
      "meta"
     ],
     "properties": {
      "data": {
       "type": "object",
       "properties": {
        "result": {
         "type": [
          "object",
          "null"
         ],
         "properties": {
          "number": {
           "type": "string"
          },
          "gasUsed": {
           "type": "string"
          },
          "gasLimit": {
           "type": "string"
          },
          "timestamp": {
           "type": "string"
          },
          "transactions": {
           "type": "array",
           "items": {
            "type": "object",
            "properties": {
             "to": {
              "type": "string"
             },
             "gas": {
              "type": "string"
             },
             "from": {
              "type": "string"
             },
             "hash": {
              "type": "string"
             },
             "nonce": {
              "type": "string"
             },
             "value": {
              "type": "string"
             }
            }
           }
          }
         }
        }
       },
       "description": "Endpoint-specific response payload"
      },
      "meta": {
       "type": "object",
       "required": [
        "endpoint",
        "request_id"
       ],
       "properties": {
        "endpoint": {
         "type": "string"
        },
        "cost_usdc": {
         "type": "string"
        },
        "request_id": {
         "type": "string"
        },
        "payment_chain": {
         "type": "string"
        },
        "payment_token": {
         "type": "string"
  
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/skills-onesource-io-f2b6b131/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from skills.onesource.io](https://www.zero.xyz/host/skills.onesource.io/llms.txt)