openapi: 3.2.0
info:
  title: BuiltWith x402 Pay-per-Call Website Search API
  version: 1.0.0
  description: Accountless pay-per-call website, company, and technology intelligence using x402 v2 and USDC on Base. AgentCash-compatible clients can discover and pay for every operation in this document.
  contact:
    name: BuiltWith Support
    email: support@builtwith.com
    url: https://builtwith.com/contact
  x-guidance: For one-off agent research, choose the narrowest /agent operation and use its documented HTTP method and input. Every /agent operation costs $0.0495; GET /agent/domain accepts query parameters and the other /agent calls accept JSON bodies. No account, API key, payer field, or prepaid key is needed. Send the intended input on the first request, read the x402 v2 challenge from PAYMENT-REQUIRED, sign it for Base USDC, and retry the identical request with PAYMENT-SIGNATURE. Validation and upstream failures are not settled. Use /agent/company-domains before /agent/domain when only a company name is known, /agent/technology-search to resolve a concept to BuiltWith technology names, and /agent/ask for natural-language website discovery. High-volume callers may instead buy prepaid credits through the BuiltWith MCP server. Fixed-price List passes are separate products for List API and committed Ask access.
servers:
- url: https://api.builtwith.com
tags:
- name: Website Search
paths:
  /agent/ask:
    post:
      operationId: askForWebsites
      summary: Find websites with a natural-language query
      description: Run an uncommitted BuiltWith Ask query and return matching websites for research and qualification. This route does not create a persistent List report.
      tags:
      - Website Search
      security: []
      x-payment-info:
        price:
          mode: fixed
          currency: USD
          amount: '0.0495'
        protocols:
        - x402: {}
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              additionalProperties: false
              properties:
                query:
                  type: string
                  minLength: 1
                  maxLength: 1000
                  description: Natural-language description of the websites to find.
                meta:
                  type: boolean
                  default: false
                  description: Include additional BuiltWith metadata when available.
              required:
              - query
            example:
              query: Magento websites in Spain
              meta: true
      responses:
        '200':
          description: BuiltWith result returned after payment settlement
          headers:
            PAYMENT-RESPONSE:
              description: Base64-encoded x402 v2 settlement response.
              schema:
                type: string
          content:
            application/json:
              schema:
                type: object
                description: BuiltWith API JSON response. Fields vary by capability and available data.
                additionalProperties: true
        '400':
          description: Invalid JSON input; verified payments are not settled for validation failures
        '402':
          description: Payment Required
          headers:
            PAYMENT-REQUIRED:
              description: Base64-encoded x402 v2 payment requirements.
              schema:
                type: string
        '502':
          description: The upstream BuiltWith API request failed; the verified payment is not settled
        '503':
          description: x402 payments are not configured on this server
externalDocs:
  description: BuiltWith x402 USDC API documentation
  url: https://api.builtwith.com/x402-api
x-discovery:
  ownershipProofs:
  - '0x1ce9d8b85fd8afc523d26bf39eb4080326e4bef016e430f327d1cf6779fcdfdd0302f8e8804599bb3b7e254f26cf7fa3bc6c1311f9c9ae190e0c70e37fb305c11b'
x-x402-discovery: https://api.builtwith.com/.well-known/x402
x-agentcash-guidance:
  llmsTxtUrl: https://api.builtwith.com/llms.txt