Monitoring · x402 · early usage

Compute the Keccak-256 hash of a Solidity function or event signature and derive the 4-…

by api.duoleads.com · discovered, not yet claimed by its owner · updated 2026-10-01

30d calls2

30d payers1

MethodGET

Outputjson

Mirrored from Coinbase's public x402 Bazaar. The description is the provider's own text and has not been reviewed here; the payment requirements are copied as published.

What it does

Compute the Keccak-256 hash of a Solidity function or event signature and derive the 4-byte function selector and the 32-byte event topic. Normalises the signature first — strips parameter names, expands uint to uint256 and the other aliases, flattens tuples — so a signature copied from source code produces the same selector as the canonical form. Also hashes arbitrary text or hex bytes with Keccak-256.

Tags: deterministic · no-api-key · chain · blockchain · solidity · bazaar

Call contract

Method: GET
Input: query parameters
Output: json
Last paid call: 2026-10-01

Input example from Bazaar metadata

{
  "signature": "transfer(address,uint256)"
}

Output example

{
  "data": {
    "canonical": "transfer(address,uint256)",
    "inputs": [
      "address",
      "uint256"
    ],
    "keccak256": "0xa9059cbb2ab09eb219583f4a59a5d0623ade346d962bcd4e46b11da047c9049b",
    "normalisations": [],
    "selector": "0xa9059cbb",
    "topic0": null
  },
  "meta": {
    "computed_at": "2026-09-28T12:00:00.000Z",
    "deterministic": true,
    "disclaimer": "Factual output of a deterministic computation over public data. Provided as is, with no warranty of accuracy, completeness or availability. Not investment, financial, legal, tax, medical or any other professional advice, and not a recommendation. Verify before relying on it. Terms: https://api.duoleads.com/terms",
    "price_usd": "0.05",
    "request_id": "01K6B7Q4ZC8H3F2M9WXR5TYN0D"
  },
  "ok": true,
  "route": "/v1/chain/selector",
  "version": "1.0.0"
}

Use with an agent

Discover. Agents find this listing with GET https://bazaar.saylorinnovations.com/discovery/search?query=…, the MCP tool search_resources, or /discovery/resources.
Inspect. Fetch /resources/36306.json for the price and payment options.
Pay. Call GET https://api.duoleads.com/v1/chain/selector. The provider answers 402 with its payment requirements. An x402 client signs one of the options below and retries with PAYMENT-SIGNATURE.
Execute. The provider returns 200 with the data. Agent Bazaar is not in the request path and never sees your payment.

For humans

You don't need an account or an API key; you need a wallet holding a small amount of USDC on Base, and an x402-capable client (see the examples below). Call the endpoint unpaid first to see exactly what it asks for.

Pricing & payment

Price: $0.05 / request
Protocol: x402 v2
Auth: No account or API key. Pay per request.
Networks: Base
Demand: 2 calls · 1 unique payers in 30d (public x402 Bazaar data)

x402 payment requirements

Scheme	Network	Asset	Amount	Pay to	Timeout
exact	Base eip155:8453	USDC	$0.05	0xCD673f7e1daD254347AEab6be0DEFe8b9C6b3A39	120s

accepts[] (raw JSON)

[
  {
    "scheme": "exact",
    "network": "eip155:8453",
    "payTo": "0xCD673f7e1daD254347AEab6be0DEFe8b9C6b3A39",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "amount": "50000",
    "amountUsd": 0.05,
    "maxTimeoutSeconds": 120
  }
]

Schemas

Output schema (JSON Schema)

{
  "properties": {
    "example": {
      "properties": {
        "data": {
          "properties": {
            "canonical": {
              "type": [
                "string",
                "null"
              ]
            },
            "encoding": {
              "type": "string"
            },
            "input_bytes": {
              "type": "integer"
            },
            "inputs": {
              "items": {
                "type": "string"
              },
              "type": [
                "array",
                "null"
              ]
            },
            "keccak256": {
              "type": "string"
            },
            "normalisations": {
              "items": {
                "properties": {
                  "from": {
                    "type": "string"
                  },
                  "to": {
                    "type": "string"
                  }
                },
                "required": [
                  "from",
                  "to"
                ],
                "type": "object"
              },
              "type": "array"
            },
            "selector": {
              "type": [
                "string",
                "null"
              ]
            },
            "topic0": {
              "type": [
                "string",
                "null"
              ]
            }
          },
          "required": [
            "canonical",
            "keccak256",
            "selector",
            "topic0",
            "inputs",
            "normalisations"
          ],
          "type": "object"
        },
        "meta": {
          "properties": {
            "computed_at": {
              "description": "RFC 3339 UTC with milliseconds",
              "type": "string"
            },
            "deterministic": {
              "type": "boolean"
            },
            "disclaimer": {
              "type": "string"
            },
            "price_usd": {
              "type": "string"
            },
            "request_id": {
              "type": "string"
            },
            "sources": {
              "items": {
                "required": [
                  "id",
                  "version",
                  "published"
                ],
                "type": "object"
              },
              "type": "array"
            }
          },
          "required": [
            "request_id",
            "computed_at",
            "price_usd",
            "deterministic",
            "disclaimer"
          ],
          "type": "object"
        },
        "ok": {
          "const": true
        },
        "route": {
          "const": "/v1/chain/selector"
        },
        "version": {
          "type": "string"
        }
      },
      "required": [
        "ok",
        "route",
        "version",
        "data",
        "meta"
      ],
      "type": "object"
    },
    "type": {
      "type": "string"
    }
  },
  "required": [
    "type"
  ],
  "type": "object"
}

Example shape — generated from the schema, not a captured live response

{
  "example": {
    "data": {
      "canonical": "string",
      "encoding": "string",
      "input_bytes": 0,
      "inputs": [
        "string"
      ],
      "keccak256": "string",
      "normalisations": [
        {
          "from": "string",
          "to": "string"
        }
      ],
      "selector": "string",
      "topic0": "string"
    },
    "meta": {
      "computed_at": "string",
      "deterministic": true,
      "disclaimer": "string",
      "price_usd": "string",
      "request_id": "string",
      "sources": [
        {}
      ]
    },
    "ok": null,
    "route": null,
    "version": "string"
  },
  "type": "string"
}

Examples

curl

curl "https://api.duoleads.com/v1/chain/selector"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid

JavaScript

const res = await fetch("https://api.duoleads.com/v1/chain/selector");
if (res.status === 402) {
  const { accepts } = await res.json();
  // pay one of accepts[] via an x402 client, then retry with the payment header
}

Python

import httpx
res = httpx.get("https://api.duoleads.com/v1/chain/selector")
if res.status_code == 402:
    accepts = res.json()["accepts"]
    # pay one of accepts[] via an x402 client, then retry with the payment header

Details

Provider: api.duoleads.com
Endpoint: https://api.duoleads.com/v1/chain/selector
Machine-readable: /resources/36306.json