openapi: 3.2.0
info:
  title: BuiltWith x402 Pay-per-Call Company Research 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: Company Research
paths:
  /agent/relationships:
    post:
      operationId: findRelatedWebsites
      summary: Find websites related to a domain
      description: Find domains related through shared identifiers, infrastructure, analytics, ownership signals, and other BuiltWith relationship evidence.
      tags:
      - Company Research
      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:
                domain:
                  type: string
                  minLength: 1
                  maxLength: 253
                  description: Domain name to research, for example example.com. Do not include a URL path.
              required:
              - domain
            example:
              domain: example.com
      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
  /agent/company-domains:
    post:
      operationId: findCompanyDomains
      summary: Find domains associated with a company name
      description: Resolve a company or brand name to associated website domains before running domain-level research.
      tags:
      - Company Research
      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:
                company:
                  type: string
                  minLength: 1
                  maxLength: 200
                  description: Company or brand name.
              required:
              - company
            example:
              company: HotelsCombined
      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
  /agent/tags:
    post:
      operationId: findDomainsByTag
      summary: Find related domains from an IP address or attribute
      description: Return domains connected to a BuiltWith tag such as an IP address or infrastructure attribute.
      tags:
      - Company Research
      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:
                lookup:
                  type: string
                  minLength: 1
                  maxLength: 300
                  description: BuiltWith tag or attribute, for example IP-75.126.76.154.
              required:
              - lookup
            example:
              lookup: IP-75.126.76.154
      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
  /agent/company-identifiers:
    post:
      operationId: getCompanyIdentifiers
      summary: Get public company identifiers for a domain
      description: Return public company registration, tax, and VAT identifiers associated with one domain when available.
      tags:
      - Company Research
      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:
                domain:
                  type: string
                  minLength: 1
                  maxLength: 253
                  description: Domain name to research, for example example.com. Do not include a URL path.
              required:
              - domain
            example:
              domain: example.com
      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