# PayAPI Market: Full Site Content

> Single-file dump of every public marketing page on payapi.market, intended for LLM ingestion. For the indexed/structured version see https://payapi.market/llms.txt

Last updated: 2026-09-11
Founder: Chet Parker
Launched: April 2026

---

## Page: Home, https://payapi.market/

# PayAPI Market: Paid APIs for AI Agents

The marketplace for x402-powered APIs. AI agents discover and pay for paid APIs per request in USDC, with no API keys, no subscriptions, and no signup. Providers list once and keep 100% of every settlement.

PayAPI Market is built for the agent economy. Every listed API speaks the Model Context Protocol (MCP) for discovery and the x402 protocol for payment. An autonomous AI agent, such as Claude Desktop, Cursor, or a custom LangChain or AutoGen agent, connects to the free catalogue MCP server at https://payapi.market/mcp, searches every listing in the marketplace, and then pays each provider directly in USDC on Base against that provider's own x402 challenge. No API keys to manage. No monthly subscriptions. No chargebacks.

### Live catalogue (2026-09-11)

147 live APIs across 983 endpoints from 79 providers. Of these, 130 are settlement-verified: a real on-chain USDC payment settled on Base for a real product response, checkable by anyone. 121 come from independent providers (69 of them); the other 9 are first-party APIs operated by PayAPI Market, labelled as such and counted separately.

| API | Provider | Category | Price (USDC) | Settlement-verified |
|---|---|---|---|---|
| 10x402 | 10x402 | Verification | $0.004-$0.12 | yes |
| 402Signal | Ross | Verification | $0.003 | yes |
| Aegis by Boris Inc | Boris Inc | Verification | $0.005-$0.25 | yes |
| AeroCheck | LoneStarOracle | Verification | $0.05 | yes |
| Agent Mercantile | Agent Mercantile | Tools | $0.01 | yes |
| Agent Utility Network (AveDaris) | AveDaris | Data | $0.001-$0.04 | yes |
| Agent402.Tools | Agent402.Tools | Tools | $0.001-$3.3 | yes |
| AGENTUM Taxas Brasil | AGENTUM LTDA | Finance | $0.01 | yes |
| Anicca x402 Agent APIs | Anicca | Intelligence | $0.005-$0.01 | yes |
| API Acre | API Acre | Tools | $0.001-$0.25 | yes |
| Autocash Text Metrics | Benjamin Dorey | Data | $0.001 | yes |
| Bankruptcy Filing Search & Chapter 11 Dockets API | AutoScrape | Data | $0.01 | yes |
| Brazil CNPJ Business Verification API | AGENTUM LTDA | Data | $0.02 | yes |
| Broken Link Checker, 404 Audit & Link Rot API | AutoScrape | Tools | $0.01 | yes |
| Building Permits Roof Age Solar AHJ Evidence API | AutoScrape | Data | $0.01 | yes |
| Bulk Email Validation & Verification API | AutoScrape | Verification | $0.01 | yes |
| Bulk HTTP Status Checker & Redirect API | AutoScrape | Tools | $0.01 | yes |
| Butterfly Delta Exact-Order Preflight | Butterfly Delta | Finance | $0.01 | yes |
| California Contractor License Lookup & Verification API | AutoScrape | Verification | $0.01 | yes |
| ChainVerdict | Alexander Balieu | Verification | $0.001-$0.1 | yes |
| Cloud World Model | Kevin Brown | Tools | $0.001-$0.005 | yes |
| CMS Nursing Home Care Compare, Ratings & Staffing API | AutoScrape | Data | $0.01 | yes |
| Cognilode Agent Security Scorer | Cognilode | Verification | $0.02 | yes |
| Cognilode Ticket Resale Underwriter | Cognilode | Finance | $0.005 | yes |
| Compute Revenue Gateway | 三流 (Sanliu) | Finance | $0.001 | yes |
| Congress Stock Trades & Financial Disclosures API | AutoScrape | Data | $0.01 | yes |
| Contract Powers | Operated by Ofir Baranes - no legal entity | Verification | $0.05 | yes |
| Council of AI GSPC — EU Evidence Feed | CSOAI Ltd | Data | $0.02 | yes |
| CourtListener Legal Opinions & Case Law API | AutoScrape | Data | $0.01 | yes |
| Crypto Snapshot Pro - AI Trading Signals | Vitali Matros | Finance | $0.025 | yes |
| CSV Drift Evidence | Foundry | Data | $0.015 | yes |
| Currency & Crypto API | PayAPI Market | Data | $0.001 | yes |
| Dallas County Property Tax Records & Assessed Value API | AutoScrape | Data | $0.01 | yes |
| DELTA Witness | DELTA Witness | Verification | $0.03 | yes |
| DELTA Witness Capture | Ruphus Sten Studio | Verification | $0.03 | yes |
| Diagram Generation API | James White | Tools | $0.05-$0.07 | yes |
| DNS & Domain Intelligence API | PayAPI Market | Intelligence | $0.002 | yes |
| Dokimo Verify API | Augaster | Verification | $0.01 | yes |
| DOL Form 5500 401(k) & Employee Benefit Plan Leads API | AutoScrape | Data | $0.01 | yes |
| Earn Agent Tools | Earn Agent Tools | Tools | $0.003 | yes |
| Email Verification API | PayAPI Market | Verification | $0.001 | yes |
| Exo Trust Synergy x402 utility layer | Exo Trust | Data | $0.002 | yes |
| FDA 510k Medical Device Clearances API | AutoScrape | Data | $0.01 | yes |
| FDA Investigations Operations Manual API | Levi Painter | Data | $0.01 | yes |
| Federal Court Dockets & PACER RECAP API | AutoScrape | Data | $0.01 | yes |
| Federal Register Rules, Regulations & Proposed Rules API | AutoScrape | Data | $0.01 | yes |
| Flat-rate LLM and EVM toolkit | AutomatIA · Automatizaciones | Tools | $0.005 | yes |
| FMCSA Carrier Safety, Inspections, Violations & Crash Data API | AutoScrape | Data | $0.01 | yes |
| GenTech Labs x402 Gateway | GenTech Labs | Finance | $0.001-$0.1 | yes |
| Genuine Good Grants API | Genuine Good | Data | $0.05 | yes |
| HALOWERK EV Charging | HALOWERK | Data | $0.005 | yes |
| HMDA Mortgage Loan Applications & Fair Lending Data API | AutoScrape | Data | $0.01 | yes |
| IP Geolocation API | PayAPI Market | Data | $0.001 | yes |
| IRS 990 Nonprofit Charity Grant Evidence API | AutoScrape | Data | $0.01 | yes |
| IRS Internal Revenue Bulletin API | Levi Painter | Data | $0.01 | yes |
| Kallipolis Proof | Kallipolis Proof | Verification | $0.01 | yes |
| kino402 | kino402 | Tools | $0.008-$16.701 | yes |
| Kristo Intelligence — DeFi Signals API | Dimitri Hristov | Finance | $0.005 | yes |
| Kurage FX Brain | bittensorman | Finance | $0.05 | yes |
| LaborPulse | LoneStarOracle | Data | $0.05 | yes |
| Lemon Toolshed | Lemon Agent | Tools | $0.002-$0.006 | yes |
| LLM2API - Gemma 4 12B + Crypto Trade Checks | bittensorman | Finance | $0.05 | yes |
| Macaroon Cyber Vulnerability Risk Search | MacaroonNetwork | Data | $0.003 | yes |
| Macaroon grant and tender search | MacaroonNetwork | Data | $0.005 | yes |
| Macaroon research paper search | MacaroonNetwork | Data | $0.001 | yes |
| MachineMint — Unsigned Base Transaction Preflight | caleb henry | Verification | $0.01 | yes |
| MacroPulse | LoneStarOracle | Finance | $0.05 | yes |
| Marketplace for AI Agents | Marketplace for AI Agents | Data | $0.005 | yes |
| Massive | Ian | Finance | $0.01 | yes |
| Melssa | Toma Tomov | Data | $0.01-$2 | yes |
| Merchant Risk WHOIS Domain Evidence API | AutoScrape | Data | $0.01 | yes |
| Moneytest x402 Agent Utilities | Moneytest | Tools | $0.001-$10 | yes |
| New Jersey UCC Lien Search & Debtor Filings API | AutoScrape | Data | $0.01 | yes |
| NexusEval Marketing Preflight | NexusEval | Verification | $0.01 | yes |
| NHTSA Vehicle Complaints & Auto Defect Reports API | AutoScrape | Data | $0.01 | yes |
| NHTSA VIN Decoder, Bulk Vehicle Specs & vPIC API | AutoScrape | Data | $0.01 | yes |
| NPPES NPI Registry & Healthcare Provider Lookup API | AutoScrape | Data | $0.01 | yes |
| OFAC SDN Sanctions Screening API | AutoScrape | Data | $0.01 | yes |
| Official Source Evidence | RegulaVita | Data | $0.01-$9 | yes |
| Official US Business Registry Evidence API | AutoScrape | Data | $0.01 | yes |
| OptionsFlow | LoneStarOracle | Finance | $0.05 | yes |
| OSHA Workplace Inspections, Violations & Penalties API | AutoScrape | Data | $0.01 | yes |
| Parallax | Parallax | Data | $0.01-$0.05 | yes |
| penny402 | penny402 | Tools | $0.0025 | yes |
| PennyAPI Local Business & Places Search | PennyAPI | Data | $0.004 | yes |
| PHION Evidence Engine | PHION Systems | Verification | $0.004 | yes |
| Phone Validation & Geocoding API | AutoScrape | Verification | $0.01 | yes |
| PlantPair API | Manowar Online | Data | $0.003 | yes |
| pogo-tb.nl -- Dutch Open Data (RDW/BAG/OV) | Above Venture | Data | $0.001-$0.01 | yes |
| Postcode & Address Lookup API | PayAPI Market | Data | $0.001 | yes |
| PreFlight Checker | Ash Ops | Data | $0.02-$0.05 | yes |
| ProfitCollector Utility API | Sami Bakhour | Data | $0.005 | yes |
| ProofForge | Black Knight Technologies | Verification | $0.01 | yes |
| Proofwork x402 Evidence APIs | Proofwork | Verification | $0.01-$0.02 | yes |
| ProviderSignal Dental Market Intelligence | Braman Analytics LLC | Data | $0.5-$2.5 | yes |
| QR Code API | PayAPI Market | Tools | $0.001 | yes |
| RatesPulse | LoneStarOracle | Finance | $0.05 | yes |
| SAM.gov Contract Opportunities & GovCon Leads API | AutoScrape | Data | $0.01 | yes |
| SameDayDesk Machine Commerce APIs | SameDayDesk | Finance | $0.002-$0.25 | yes |
| SanctionsScreen | LoneStarOracle | Verification | $0.05 | yes |
| Saymon RU Data API | Real Energy Ltd | Data | $0.01-$0.05 | yes |
| Scamalytics IP Address Fraud Risk Score | Scamalytics | Data | $0.01 | yes |
| Schema Markup, JSON-LD & Structured Data Extractor API | AutoScrape | Tools | $0.01 | yes |
| Screenshot & PDF Capture API | PayAPI Market | Intelligence | $0.002 | yes |
| SEC EDGAR Filings Public Company Evidence API | AutoScrape | Data | $0.01 | yes |
| SEC Form 13F Institutional & Hedge Fund Holdings API | AutoScrape | Data | $0.01 | yes |
| SEC Form 8-K Material Events, Earnings & M&A API | AutoScrape | Data | $0.01 | yes |
| SEC Form D Startup Funding & Private Placement API | AutoScrape | Data | $0.01 | yes |
| Sirenic | Sirenic | Data | $0.001-$0.5 | yes |
| Sitemap URL Extractor & XML Sitemap Parser API | AutoScrape | Tools | $0.01 | yes |
| Skim - Clean Reader API | Skim | Tools | $0.002-$0.02 | yes |
| Sunbiz Florida New Business Filings & LLC Leads API | AutoScrape | Data | $0.01 | yes |
| The Clinic | Sap Thumbprint | Tools | $0.001 | yes |
| TinyOps Automation Integration Preflight | TinyOps Studio LLC | Verification | $0.03-$0.1 | yes |
| TradeRails | Alexander Balieu | Verification | $0.004-$0.05 | yes |
| Trend Signals | TrendSignals | Finance | $0.001-$0.05 | yes |
| UK HMO Licence API | PayAPI Market | Data | $0.02-$0.04 | yes |
| ukintel.uk | ukintel | Data | $0.005-$0.2 | yes |
| US Tariff HTS Code Lookup & Import Duty API | AutoScrape | Data | $0.01 | yes |
| Validated Scientific Solver Index | MacaroonNetwork | Data | $0.005 | yes |
| Web Scraper & Content Extractor API | PayAPI Market | Tools | $0.002 | yes |
| Web Search & Data API — SERP, page reader & scrapers | kadec0 | Data | $0.005-$0.15 | yes |
| Website Company Enrichment & Domain Intelligence API | AutoScrape | Data | $0.01 | yes |
| Website Tech Stack Scanner & BuiltWith Alternative API | AutoScrape | Tools | $0.01 | yes |
| x402 MCP Tools | Alex Carter | Tools | $0.01-$0.02 | yes |
| x402.freeq.one | InApp | Tools | $0.001-$0.005 | yes |
| x402pulse | Alexander Balieu | Intelligence | $0.03-$0.5 | yes |
| Yahoo Finance Stock Data & Historical Prices API | AutoScrape | Finance | $0.01 | yes |
| zFinia Accessibility Contrast Calculator | zFinia | Tools | $0.001 | yes |
| zFinia machine_economy_changes_since | zFinia | Intelligence | $0.01 | yes |
| AgentBodega Agent Tools | AgentBodega | Tools | $0.001-$0.06 | no |
| Anchor-x402 | Anchor-x402 | Intelligence | $0.001-$1.77 | no |
| DEX Swap Quotes API | Klymax402 | Finance | $0.005 | no |
| ENS Resolver API | Klymax402 | Tools | $0.002 | no |
| Hyperliquid Perp Market Data API | Klymax402 | Data | $0.001-$0.002 | no |
| IRONCLAW BTC Node | BTC Node | Data | $0.001-$0.01 | no |
| M2M Trust Lean Six Sigma API | Energy Bill Toolkit | Tools | $0.001 | no |
| OSS2API Multi-skill Agent API | bittensorman | Tools | $0.01 | no |
| Research Brief API (x402) | Devvizion | Intelligence | $0.01-$0.02 | no |
| StockWaves | TANG | Finance | $0.03-$0.5 | no |
| TensorFeed | TensorFeed | Data | $0.02-$0.06 | no |
| Text Metrics API | Energy Bill Toolkit | Tools | $0.001 | no |
| Token Safety & Contract Risk API | Klymax402 | Intelligence | $0.003 | no |
| UK Air Quality API | Energy Bill Toolkit | Data | $0.001 | no |
| UK Data API | PayAPI Market | Data | $0.001-$0.002 | no |
| UK Waste Collection API | Energy Bill Toolkit | Data | $0.001 | no |
| x402 Agent-Payment Infrastructure | Wisely Enterprises LLC | Tools | $0.001-$5 | no |

Total: 147 live APIs / 983 endpoints from 79 providers; 130 settlement-verified (121 independent + 9 first-party, counted separately). Live price range $0.001-$16.701 USDC per request; settlement-verified range $0.001-$16.701 USDC.

### How it works
1. **Discovery**: Agents connect to the free catalogue MCP server at https://payapi.market/mcp (or call /agent/search over plain HTTP) and find a listing plus its base_url. Discovery is free and settles nothing.
2. **Request**: The agent calls a tool. The server responds with HTTP 402 plus x402 payment requirements (amount, recipient wallet, currency, chain).
3. **Payment**: The agent's wallet signs and broadcasts the USDC transfer on Base. ~400ms finality.
4. **Delivery**: The server verifies on-chain, returns the data.
5. **Settlement**: Providers keep 100% of every x402 settlement. USDC routes directly from the paying agent to the provider's own wallet via the CDP Facilitator. PayAPI Market never takes a cut on-chain.

### Why it matters
The agent economy needs a payment rail that does not depend on credit cards, OAuth, or quarterly contracts. Subscription pricing breaks for autonomous workloads: an agent might call your API 3 times all month or 30,000 times in an hour. Per-request micropayments in stablecoin solve both: providers get paid for actual use, agents pay for actual value, and there is no contract negotiation.

---

## Page: Pricing, https://payapi.market/pricing

# Pricing: Free to list, you keep 100%

Two tiers. No subscriptions for buyers. No monthly fees on the free tier.

### Free, $0 / forever
- No per-request fee on successful x402 calls
- 100% of every settlement retained by the provider
- Unlimited API listings
- Per-request USDC payouts (settled on-chain, no invoicing)
- Discoverable through our MCP server (/mcp) and HTTP discovery (/agent), with no key and no account
- No per-request fee: if your API earns, you keep all of it, and you never pay PayAPI Market to receive a settlement
- No monthly bill, ever

### FAQ

**Is listing really free?**
Yes. You can list any API on PayAPI Market at no cost. There is no per-request fee: you keep 100% of every settlement, so you never pay us to get paid.

**Is there a per-request fee?**
When an AI agent pays your API via x402, 100% of every settlement goes directly to your wallet. USDC routes from the paying agent to your own wallet via the CDP Facilitator, and PayAPI Market never takes a cut on-chain. No invoicing, no monthly bill, no surprise fees.

**Do I need a crypto wallet to get paid?**
Yes. Payments settle as USDC on Base. You provide a wallet address at listing time. Off-ramp to USD is available through any USDC-supported exchange or bank on-ramp like Coinbase.

**Can I change pricing per endpoint?**
Yes. Every endpoint can have its own x402 price, from $0.0001 to any amount. Price per request is set in your MCP server configuration; the marketplace reads and displays it automatically.

**Do buyers pay monthly subscriptions?**
No. The whole point of x402 is pay-per-request. AI agents pay only for the calls they make, in USDC, with no minimum spend and no accounts. This makes your API instantly usable by any agent on the network.

---

## Page: About, https://payapi.market/about

# About PayAPI Market

PayAPI Market exists because the API economy was built for humans clicking through OAuth flows and pasting bearer tokens, and AI agents are fundamentally different customers. Agents are autonomous, they do not have credit cards, they discover tools at runtime, and their request volume is bursty in ways that break subscription pricing. The agent economy needs a marketplace that speaks the agent's protocols.

### What we believe
- Per-request stablecoin payments are the right primitive for autonomous workloads
- Discovery should happen at runtime via MCP, not at design-time via human-curated docs
- Marketplaces should take as little as possible: PayAPI Market takes nothing per request, so providers keep 100%, which beats RapidAPI's complex tier structure
- Open protocols (x402, MCP, USDC) beat closed platforms

### Founder
PayAPI Market was built by Chet Parker. Launched April 2026.

### How we got here
The x402 status code was defined in HTTP/1.0 in 1996 and then sat largely unused for decades, because there was no good way to settle micropayments. Stablecoins on fast L2 chains changed the economics: USDC on Base settles in ~400ms with sub-cent fees. That made x402 viable. Then Anthropic published MCP in late 2024 as a standard way for LLMs to discover and call tools. The intersection of those two protocols is what made PayAPI Market possible: MCP for discovery, x402 for payment, USDC for settlement.

---

## Page: Calculator, https://payapi.market/calculator

# Revenue Calculator

Estimate what your API could earn on PayAPI Market.

### Inputs
- Number of endpoints
- Average price per request (USDC)
- Estimated requests per month

### Outputs
- Gross monthly revenue (paid straight to your wallet, no fee deducted)
- Annual run rate

### Worked example
A property data API with 24 endpoints averaging $0.002/request, doing 50,000 requests/month:
- Gross: $100/month
- You keep $100/month, so $1,200/year. There is no per-request fee and no listing fee.

A crypto pricing API with 15 endpoints averaging $0.001/request, doing 500,000 requests/month:
- Gross: $500/month
- You keep $500/month, so $6,000/year

A geocoding API doing 5,000,000 requests/month at $0.0005:
- Gross: $2,500/month
- You keep $2,500/month, so $30,000/year

---

## Page: For Providers, https://payapi.market/providers

# For API Providers

Monetise your API for the agent economy in 10 minutes. No payment integration to build, no billing system to maintain, no chargebacks to dispute.

### What you need
1. A working API with at least one endpoint
2. An MCP server in front of it (we provide a wrapper template)
3. A USDC wallet on Base
4. A description of what your API does

### What we handle
- x402 payment verification (the MCP wrapper handles HTTP 402 responses)
- USDC settlement on-chain (every successful call routes directly to the provider's wallet via the CDP Facilitator; PayAPI Market never takes a cut on-chain)
- Discovery (your tools appear in the MCP manifest agents query)
- Search ranking (boosted by uptime, latency, and request volume)
- Health monitoring (a scheduled check pings each listing's /health endpoint, falling back to the root URL, counts an x402 402 response as healthy, and tracks a rolling uptime percentage per listing)

### Listing flow
1. Sign up at https://payapi.market/list
2. Provide your name, email, wallet address, and API URL
3. Submit for review
4. Once approved, your API is live and discoverable by every agent on the network

---

## Page: For Agents, https://payapi.market/agents

# For AI Agents

PayAPI Market is the easiest way for an agent to find and pay for real-world data and tools. One MCP endpoint, dozens of APIs, USDC settlement.

### Connecting from Claude Desktop
Add to your `claude_desktop_config.json`:
```json
{
  "mcpServers": {
    "payapi": {
      "url": "https://payapi.market/mcp"
    }
  }
}
```

Restart Claude Desktop. You get three discovery tools: search_apis, list_apis and get_api. Discovery is free; paying happens on the listing's own 402, called directly against the provider. Separately and optionally, https://web-production-18a32.up.railway.app/mcp/sse is a different first-party server exposing the UK property tools only, and its tools/call is paid.

### Connecting from Cursor / Continue / custom agents
Any MCP-compatible client works. Point it at the same SSE endpoint above.

### Paying for calls
Your client needs to:
1. Have a USDC wallet on Base with a small balance
2. Handle HTTP 402 responses by signing and broadcasting the requested payment
3. Retry the request with proof of payment

The official x402 client libraries (TypeScript, Python, Rust) handle this automatically. Total per-call latency including payment is ~500-800ms.

### Why this matters for agents
Subscription APIs are unusable for agents. You do not know in advance whether you will need 5 calls or 50,000, you cannot sign up for a $99/month plan when each user session might justify $0.02 of API spend, and you cannot manage 50 different API keys across 50 different vendors. PayAPI Market collapses all of that into a single MCP endpoint and a USDC wallet.

---

## Page: For Developers, https://payapi.market/developers

# For Developers

Build agents, build wrappers, contribute to the ecosystem.

### Quick links
- x402 protocol spec: https://github.com/coinbase/x402
- MCP spec: https://modelcontextprotocol.io
- PayAPI Market open API listing endpoint: https://payapi.market/api/listings
- Marketplace MCP endpoint: https://payapi.market/mcp (free discovery: search_apis, list_apis, get_api)
- First-party UK property MCP, a separate server with paid tools/call: https://web-production-18a32.up.railway.app/mcp/sse

### SDK availability
- TypeScript: x402-fetch (npm)
- Python: x402-httpx (pip)
- Rust: x402-reqwest (crates.io)

### How to wrap an existing API for x402
The PayAPI Market team maintains an open-source x402-MCP wrapper template. It is a small Express server that:
1. Sits in front of your existing API
2. Returns HTTP 402 with payment requirements on each request
3. Verifies the payment proof (a transaction hash plus signature)
4. Forwards the request to your real API
5. Returns the response

You can deploy it to Railway, Fly, Vercel, or any Node host in under 10 minutes.

---

## Page: For Enterprises, https://payapi.market/enterprises

# For Enterprises

PayAPI Market is the distribution layer for enterprise data products that want to reach the agent ecosystem without building their own marketplace.

### Use cases
- **Data vendors**: bring your existing dataset (financial, geospatial, regulatory) to autonomous agents without building a separate billing stack
- **API monetisation**: turn an internal API into external revenue with on-chain settlement (no AR, no invoicing, no collections)
- **Compliance APIs**: sell verification and compliance lookups (KYC, sanctions, GDPR) priced per request
- **Real-time data**: sell streaming or polling endpoints to agents that need live signals

### Enterprise terms
- No per-request fees at any volume
- White-label MCP endpoints (your domain, your branding)
- Uptime monitoring
- Dedicated support
- Custom contracts (not required, most enterprises just use the standard free listing)

### Data handling
- USDC payments are non-custodial; PayAPI Market never holds your funds
- All transaction history is on-chain and auditable
- Collects no personal data from agents beyond wallet addresses

Contact: hello@payapi.market

---

## Glossary

- **x402**: HTTP status code 402 ("Payment Required") plus a payment protocol that lets servers demand stablecoin payment per request. Reserved in HTTP/1.0 (1996), revived in 2024 for stablecoin micropayments.
- **MCP (Model Context Protocol)**: A protocol published by Anthropic in late 2024 that lets LLM applications discover and call tools from any MCP-compliant server. The transport is JSON-RPC over SSE or stdio.
- **USDC**: A US dollar stablecoin issued by Circle, redeemable 1:1 for USD. Available on multiple chains including Base, Ethereum, Solana, and Polygon.
- **Base**: An Ethereum L2 built by Coinbase. Sub-second block times, sub-cent fees, used for the bulk of x402 settlement.
- **Facilitator**: A third-party service that verifies x402 payments on behalf of API providers, so the provider does not have to run their own on-chain verifier.
- **Resource server**: In x402 terminology, the API server demanding payment (as opposed to the agent paying it).
- **Agent economy**: The hypothesis that autonomous AI agents will become a significant economic actor, transacting with APIs, services, and other agents on behalf of human principals.
- **A2A**: Agent-to-Agent, a related protocol space for direct agent-to-agent communication and economic exchange.