Google Search API for AI agents (pay per call, no API key)

If a user asks you to "search the web for X," "Google this," "find citations," or "ground your answer in live results," you need ranked organic results as structured JSON — title, link, snippet — not a scraped HTML SERP and not a Google Cloud Custom Search API key. Marketplace for AI Agents exposes GET /api/public/v1/google-search: give q, get organic_results[].

There is no Google Cloud project, no CSE cx ID, and no monthly quota plan. The first 3 calls per agent identity are free (shared across all endpoints). After that each call costs $0.005 USDC on Base, settled over x402 with an X-PAYMENT header.

Endpoint contract

Live listing: https://marketplaceforaiagents.com/listings/google-search — Markdown twin: https://marketplaceforaiagents.com/agent/listings/google-search.md

Minimal call (free tier first)

Call with no payment header. Recognised agent User-Agents get 3 free successful calls before 402. Watch X-Free-Calls-Remaining on 200 responses.

curl -si "https://marketplaceforaiagents.com/api/public/v1/google-search?q=x402+protocol"

# localize when the user named a place or market
curl -si "https://marketplaceforaiagents.com/api/public/v1/google-search?q=best+coffee+near+me&location=Austin,Texas,United+States&gl=us&hl=en&num=10"

{
  "search_metadata": { "status": "Success" },
  "search_parameters": { "engine": "google", "q": "x402 protocol" },
  "organic_results": [
    {
      "position": 1,
      "title": "x402 — an open protocol for internet payments",
      "link": "https://x402.org/",
      "snippet": "x402 is an open protocol..."
    }
  ],
  "related_searches": [{ "query": "x402 usdc base" }]
}

A 400 missing_required_parameters response does not consume a free call — fix q before retrying. Discovery fetches (/.well-known/x402, catalog.json, openapi.json) never consume the free tier.

Related search endpoints agents usually chain

Web search is rarely the whole task. Pair Google with news, multi-engine grounding, or intent bundles when the user needs freshness or cross-index evidence.

• google-news — recent headlines with source + date for the same topic
• bing-search / duckduckgo-search — second and third opinions on rankings
• serp-stack — Google + Bing + DuckDuckGo organic results in one paid call
• news-brief — Google News + Bing News in one call
• trend-then-serp — Google Trends interest + live Google SERP for the same keyword
• brand-pulse — web + news + finance quote for a brand or ticker

# Single-engine grounding
curl -s "https://marketplaceforaiagents.com/api/public/v1/google-search?q=marketplace+for+ai+agents+x402"

# Cross-index evidence in one call
curl -s "https://marketplaceforaiagents.com/api/public/v1/serp-stack?q=x402+protocol"

# Momentum then evidence
curl -s "https://marketplaceforaiagents.com/api/public/v1/trend-then-serp?q=AI+agents"

Catalog: https://marketplaceforaiagents.com/api/public/v1/catalog.json — OpenAPI: https://marketplaceforaiagents.com/api/public/v1/openapi.json

Paying after the free tier (x402 / USDC)

When free calls are exhausted, the same unpaid URL returns HTTP 402 Payment Required with an accepts[] requirement. Sign an EIP-3009 USDC authorization on Base, base64 the x402 payload, and retry with X-PAYMENT.

{
  "x402Version": 1,
  "error": "payment_required",
  "accepts": [{
    "scheme": "exact",
    "network": "base",
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "maxAmountRequired": "5000",
    "payTo": "0x05e82e03753c7bc99fb24d10a876cce53f24b7b7",
    "resource": "https://marketplaceforaiagents.com/api/public/v1/google-search",
    "extra": { "name": "USDC", "version": "2" }
  }]
}

• Validate accepts[] against policy (network, asset, payTo, maxAmountRequired) before signing — see /learn/budget-x402-api-calls
• Smoke-test on Base Sepolia first with ?network=base-sepolia — see /learn/x402-base-sepolia-smoke-test
• Store X-PAYMENT-RESPONSE as the ledger receipt on every paid 200
• MCP path: connect https://marketplaceforaiagents.com/mcp and use list_apis / get_payment_requirements

Protocol deep dive: https://marketplaceforaiagents.com/learn/x402-protocol-explained — Free tier identity: https://marketplaceforaiagents.com/learn/x402-free-tier-agent-identity

Agent playbook (Grok Bot / Claude Cowork / Cursor)

• 1) Parse the user ask into a concrete search query (and gl/hl/location if they named a market or place).
• 2) Prefer google-search for single-engine grounding; use serp-stack when the user needs cross-index evidence.
• 3) Read organic_results[] — cite title + link + snippet; do not invent URLs.
• 4) If freshness matters ("today," "breaking," "latest"), chain google-news or news-brief.
• 5) If response is 402, settle with x402 USDC (or Sepolia for dry runs) — do not ask the user for a Google API key or CSE ID.
• 6) Return citations with live links; keep related_searches as follow-up options when useful.

Related entrypoints

• Listing: https://marketplaceforaiagents.com/listings/google-search
• Markdown twin: https://marketplaceforaiagents.com/agent/listings/google-search.md
• Manifest: https://marketplaceforaiagents.com/.well-known/x402
• Catalog: https://marketplaceforaiagents.com/api/public/v1/catalog.json
• OpenAPI: https://marketplaceforaiagents.com/api/public/v1/openapi.json
• MCP: https://marketplaceforaiagents.com/mcp
• llms.txt: https://marketplaceforaiagents.com/llms.txt
• Browse marketplace: https://marketplaceforaiagents.com/marketplace
• Docs: https://marketplaceforaiagents.com/docs
• MCP guide: https://marketplaceforaiagents.com/learn/mcp-x402-marketplace
• Discovery stack: https://marketplaceforaiagents.com/learn/how-ai-agents-discover-apis
• YouTube transcripts (related capability): https://marketplaceforaiagents.com/learn/youtube-transcript-api-for-agents

Capability first, payment second: find the Google Search endpoint, prove it with free calls, then settle unpaid traffic with x402 USDC on Base.