Concepts and guides for the agent economy

x402 turns HTTP 402 Payment Required into a working settlement layer for autonomous agents. Here is the handshake, the EIP-3009 USDC authorization, and why it is the wire format for agentic commerce.

A step-by-step guide to wrapping any HTTP endpoint with x402: pricing, the 402 response, verification, settlement, free tiers, and listing it in an agent API marketplace so autonomous agents can discover and pay for it.

API keys, monthly invoices, and Stripe Checkout were designed for humans. Here is a head-to-head comparison with per-call x402 settlement, and when each model still wins.

Autonomous agents do not browse marketing sites. Here is the discovery stack — llms.txt, /.well-known/x402, OpenAPI, MCP, and Markdown twins — that lets an agent find, price-check, and call a machine-payable API without a human in the loop.

A practical agent-first guide to enforcing spend policy before signing an x402 payment: validating 402 accepts[], comparing network, asset, payee, and amount against an allowlist, and recording debits only from successful payment receipts.

How an AI agent uses the Model Context Protocol to discover machine-payable APIs, read live x402 payment requirements, and call endpoints that settle in USDC on Base — without accounts or API keys.

Prove your agent can complete the x402 handshake with testnet USDC and mock responses before spending real Base mainnet USDC. Query param, assets, facilitator, and a checklist for promoting to production.

Marketplace for AI Agents gives every agent identity 3 free calls across all endpoints before x402 payment kicks in. Here is how identity is scoped, how to read X-Free-Calls-Remaining, and how to graduate to paid USDC calls without surprise 402s.

When a user asks an agent for YouTube captions or a video transcript, call a machine-payable transcript endpoint that returns JSON segments — no YouTube Data API key, no Google Cloud project, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to search the web or ground an answer with live citations, call a machine-payable Google SERP endpoint that returns organic results as JSON — no Google Cloud key, no Custom Search Engine ID, settlement via x402 USDC on Base after three free evaluation calls.

Marketplace for AI Agents is now settlement-verified on PayAPI Market: a third party paid real USDC on Base and got a real SERP response. Here is what that means for autonomous agents choosing a machine-payable Google Search, YouTube transcript, and intent API — and the exact URLs to call next.

When a user asks an agent to search Amazon, look up a product by ASIN, or compare price and reviews, call machine-payable Amazon endpoints that return JSON listings — no Amazon Product Advertising API key, no Associates account, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to find flights, compare itineraries, or sketch a trip (flights + hotels), call machine-payable Google Flights / Hotels endpoints that return priced JSON — no Google Cloud key, no travel-API signup, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to find local businesses, look up a place on a map, or pull reviews for a venue, call machine-payable Google Maps endpoints that return local_results / reviews JSON — no Google Cloud Maps key, no Places API billing account, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to find academic papers, citations, or an author's publication record, call machine-payable Google Scholar endpoints that return organic_results / articles JSON — no SerpAPI key, no Google Cloud project, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to look up iOS or Android apps, compare storefronts, or run ASO research, call machine-payable Apple App Store and Google Play endpoints that return organic_results JSON — no App Store Connect key, no Play Developer Console, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent for recent news, a morning brief, or coverage of a topic, call machine-payable Google News / Bing News endpoints that return news_results JSON — no Google Cloud News API key, no Bing Search subscription, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to compare prices, find product offers, or shop across merchants, call machine-payable Google Shopping endpoints that return shopping_results JSON — no Google Cloud Shopping API key, no merchant partner account, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to find job postings, source remote roles, or scout hiring signals, call a machine-payable Google Jobs endpoint that returns jobs JSON — no Google Cloud Jobs API key, no ATS partnership, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent for a stock quote, ticker price, index, currency, or crypto movers, call a machine-payable Google Finance endpoint that returns summary JSON — no Google Cloud Finance API key, no brokerage partnership, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to find images, diagrams, screenshots, or reverse-search a photo, call machine-payable Google Images / Lens / reverse-image endpoints that return images_results / visual_matches JSON — no Google Cloud Vision or Custom Search key, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to find hotels, compare stays, or sketch lodging for a trip (hotels + optionally flights via trip-skeleton), call machine-payable Google Hotels endpoints that return properties JSON — no Google Cloud / Places key, no OTA account, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to check keyword interest, compare search momentum, or pair trends with a live SERP, call machine-payable Google Trends endpoints that return interest_over_time JSON — no Google Cloud / Trends API key, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to compare prices across retailers, check Walmart vs Amazon vs eBay, or find the best offer, call machine-payable commerce endpoints that return organic_results / shopping_results JSON — no Walmart, Amazon PA-API, or eBay developer keys, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to search patents, scan prior art, or track competitor IP filings, call a machine-payable Google Patents endpoint that returns organic_results JSON — no SerpAPI key, no Google Cloud project, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to find concerts, conferences, meetups, or things to do in a city, call a machine-payable Google Events endpoint that returns events JSON — no Google Cloud / Places key, no ticket-API signup, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to research the Chinese, Korean, or Russian-language web — or to check what local searchers actually see — call machine-payable Baidu, Naver, and Yandex endpoints that return organic_results JSON. No Baidu developer account, no Naver Open API app, no Yandex XML key; settlement via x402 USDC on Base after three free evaluation calls.

Microsoft retired the Bing Search APIs on August 11, 2025. When a user asks an agent for Bing results, a second opinion beyond Google, or cross-engine grounding, call machine-payable bing-search, duckduckgo-search, yahoo-search, bing-news, bing-images, bing-videos, or the serp-stack intent. JSON out, no Azure subscription, no API key; settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to verify a claim, quote, statistic, or viral photo, call serp-stack, news-brief, google-scholar / scholar-pack and image-provenance for cited JSON evidence across independent indexes. No API keys; x402 USDC on Base after three free calls.

Keyword research for Grok Bot, Claude Cowork and Cursor agents: Google Autocomplete suggestions, Google Trends interest and live Google results as JSON, paid per call in USDC on Base via x402 — no account or API key.

When a user asks an agent to find YouTube videos on a topic, rank candidates, or digest the top talk into captions, call machine-payable youtube-search, youtube-video, and video-digest endpoints that return video_results / results JSON — no YouTube Data API key, no Google Cloud project, settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to monitor a brand, check what the press is saying about a company, or pull a due-diligence snapshot before a meeting, call the machine-payable brand-pulse intent (Google Search + Google News + Google Finance in one response) plus news-brief, bing-news and google-trends for a second index and momentum. JSON out, no API key, no media-monitoring seat; settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent what buyers say about a product, whether a restaurant or contractor is any good, or to flag complaint patterns before a purchase, call machine-payable amazon-reviews, google-maps-reviews, review-risk, place-dossier and deal-triage endpoints that return review text, star ratings, dates and verified-purchase flags as JSON. No Amazon PA-API key, no Google Places billing account; settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to plan a trip, find flights and hotels together, or sketch a weekend getaway with things to do, call the machine-payable trip-skeleton intent (and google-flights / google-hotels / google-events when you need a single engine) that returns priced itineraries, lodging and optional events as JSON. No Google Cloud travel key, no OTA partner account; settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to search the web across engines, ground an answer with independent citations, or get a second opinion beyond Google, call the machine-payable serp-stack intent (Google + Bing + DuckDuckGo in one response) or the single-engine google-search / bing-search / duckduckgo-search endpoints that return organic_results JSON. No Google Cloud CSE key, no Azure Bing subscription, no DuckDuckGo Instant Answer key; settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent to research a competitor (what they charge, who they are hiring, what they are patenting, how their apps rate, and whether their category is rising), call machine-payable cross-store-price, google-jobs, google-patents, aso-dual, trend-then-serp and brand-pulse endpoints that return JSON. No SerpAPI key, no LinkedIn or App Store Connect access, no market-intelligence seat; settlement via x402 USDC on Base after three free evaluation calls.

When a user asks an agent where their site ranks for a keyword, in a specific city, or across search engines, call the machine-payable google-search endpoint (location, gl, hl, num, page) or the serp-stack intent (Google + Bing + DuckDuckGo) and read position and domain from organic_results. No account or API key: 3 free calls per agent identity, then pay per call with x402 USDC on Base.

When a user asks an agent to watch a product's price, alert on a drop, or check whether a deal is real, call machine-payable amazon-product (buybox price, list price, save %, availability), google-shopping, walmart-search and ebay-search endpoints that return numeric prices as JSON. No Amazon PA-API key, no Walmart or eBay developer app; 3 free calls per agent identity, then pay per call with x402 USDC on Base.

When a user asks an agent to find video coverage of an event, a clip of a launch or product demo, or videos beyond YouTube, call machine-payable google-videos and bing-videos endpoints that return title, link, length, source, channel, date and (Google) key moments as JSON. No YouTube Data API key and no Bing Search API (retired in 2025); 3 free calls per agent identity, then pay per call with x402 USDC on Base.

When a user asks an agent to build a prospect list of local businesses (roofers in Tacoma, dentists in Austin, cafes without a website), page through machine-payable Google Maps results, dedupe by place_id, qualify with reviews, and settle each call over x402 USDC on Base - no Google Cloud key, no lead-database subscription.