Early Experimental Base HTTP 402 USDC MCP-ready Research

API20

The terminal gateway for x402-powered APIs on Base.

Discover, test, and inspect x402-powered APIs through a terminal-inspired interface built for HTTP 402 payment flows, Base USDC exploration, and future MCP-ready agent workflows.

Explore Docs View Registry Submit API
api20 — zsh
$

Scanner

Endpoint Scanner

Simulate an x402 endpoint scan to preview planned CLI behavior.

This is a simulated scanner. No real network request is made in the current static version.

URL
api20 scan — output
$ api20 scan https://server.api20.xyz/weather
Ready. Click "Scan Endpoint" to simulate.

Purpose

Why API20?

API20 is an experimental discovery and testing layer for x402-powered APIs on Base. It helps developers understand how HTTP 402 payment requirements can be inspected, documented, and explored before integrating paid APIs into agent workflows.

API discovery — Browse and preview x402-compatible APIs with pricing and metadata.

HTTP 402 inspection — Simulate how payment requirements appear before a paid request.

Base + USDC payment flow exploration — Research pay-per-request flows on Base without claiming live payment execution.

MCP-ready documentation — Prepare API metadata for future agent tool integrations.

Future agent workflows — Explore how paid APIs may connect to AI agents through MCP servers.

$ api20.xyz
─────────────────────
layer   : discovery + testing
network : Base
asset   : USDC
protocol: HTTP 402 / x402
mcp    : research / planned
builder: attribution research
status  : early experimental
→ not official · dev-first

MCP Research

MCP-ready API discovery

AI agents need reliable tools, APIs, and payment-aware workflows. API20 explores how x402-powered APIs can be discovered, documented, and prepared for future MCP server integrations. API20 is designed to help developers discover and document APIs that may later be exposed to AI agents through MCP servers.

Agent Tool Discovery

API discovery for agent tools — catalog paid endpoints with structured metadata before MCP integration.

MCP Server Research

Future MCP server compatibility research. No live MCP server is operated today.

Payment-aware API Metadata

Document network, asset, price, and protocol fields that agents need before calling a paid API.

MCP-ready Workflows

Attribution Research

Builder Codes Research

Builder Codes introduce an attribution layer for x402 payments on Base. API20 is tracking Builder Codes as future registry metadata for identifying which apps, APIs, and agent workflows may drive or serve x402 traffic.

App-level Attribution

Track which apps or builders may receive attribution for x402 settlement traffic on Base.

x402 Traffic Metadata

Document how registry entries may reference payment traffic and service attribution fields.

ERC-8021 Research

Explore ERC-8021 Schema 2 Builder Code fields as documentation-only registry metadata.

Builder Code support is currently research/planned. API20 does not attach Builder Codes to real x402 settlement transactions in the current version.

Builder Codes Research

Features

Core Features

Endpoint Scanner

Probe API endpoints and detect HTTP 402 Payment Required responses with x402-compatible headers.

Payment Requirement Inspector

Parse and display payment requirements including network, asset, amount, and resource metadata.

Base + USDC Preview

Preview how USDC-based micropayments on Base would apply to a given API request before execution.

x402 API Registry

Browse a curated preview of x402-compatible APIs with pricing, endpoints, and availability status.

Agent-ready Workflow

Designed for AI agents and automation tools that need structured payment flow discovery.

Developer-first Docs

Clear documentation covering x402 concepts, example commands, and planned CLI behavior.

Registry

x402 API Registry Preview

Browse demo API entries. Filter by category to preview how the public registry will work.

4 entries · preview mode
API Name Category Price Network Status MCP Ready Builder Code Action
Weather API Data 0.001 USDC/request Base Demo Demo Planned Details
Market Data API Finance 0.002 USDC/request Base Demo Planned Planned Details
Agent Tool API AI Agent 0.005 USDC/request Base Demo Demo Research Details
Content API Content 0.001 USDC/request Base Demo Planned Planned Details

Weather API

0.001 USDC/request

Data · Base · MCP: Demo · Builder: Planned

Market Data API

0.002 USDC/request

Finance · Base · MCP: Planned · Builder: Planned

Agent Tool API

0.005 USDC/request

AI Agent · Base · MCP: Demo · Builder: Research

Content API

0.001 USDC/request

Content · Base · MCP: Planned · Builder: Planned

Full Registry Submit API

v0.3

Registry Metadata Layer

API20 now includes a structured registry metadata layer for documenting x402-powered APIs, including endpoint details, payment requirements, MCP-ready status, Builder Code attribution research, and example HTTP 402 responses.

{
  "id": "weather-api",
  "name": "Weather API",
  "category": "Data",
  "endpoint": "https://server.api20.xyz/weather",
  "network": "base",
  "asset": "USDC",
  "price": "0.001",
  "paymentProtocol": "x402",
  "mcpReady": "demo",
  "builderCode": "planned",
  "attributionStandard": "ERC-8021 research",
  "status": "demo",
  "description": "Example paid weather endpoint using HTTP 402."
}
View Public Registry JSON API Detail Example

Schema

Registry Schema

Preview of how API20 may represent x402-powered APIs in the registry — including MCP-ready metadata fields.

{
  "name": "Weather API",
  "category": "Data",
  "endpoint": "https://api.example.com/weather",
  "network": "base",
  "asset": "USDC",
  "price": "0.001",
  "paymentProtocol": "x402",
  "mcpReady": "demo",
  "builderCode": "planned",
  "attributionStandard": "ERC-8021 Schema 2 research",
  "status": "demo",
  "description": "Example paid weather endpoint using HTTP 402."
}
View schema docs on GitHub

Workflow

How It Works

01

Request API endpoint

Send a request to any API endpoint that may require payment per call.

02

402 Payment Required

The endpoint returns HTTP 402 with x402 payment requirement headers.

03

Inspect requirements

Parse network, asset, amount, and scheme from the 402 response payload.

04

Prepare paid flow

Prepare the Base / USDC payment flow and retry the request with proof of payment.

Interactive

Command Preview

Switch between commands to preview planned CLI behavior. See full command docs for details.

$ api20 scan https://server.api20.xyz/weather

Audience

Built for

Developers

Integrate pay-per-request APIs into your stack with clear visibility into x402 payment flows and Base USDC requirements.

AI Agents

Give autonomous agents a structured way to discover, inspect, and prepare payments for x402-powered services.

API Builders

Understand how your API appears to clients when returning HTTP 402 and listing in the x402 registry.

Changelog

Release History

Honest progress tracking for an early-stage experimental project.

v0.3

Registry Metadata Layer current

Added public registry.json, API detail pages, curl examples, metadata previews, and expanded registry fields for MCP-ready workflows and Builder Code attribution research.

v0.2

Registry preview, MCP research, and scanner mock

MCP-ready workflow page, registry filters, live terminal demo, submit API form, schema preview, and updated positioning copy.

v0.1

Website launch, docs, terminal preview

Initial site, documentation, interactive terminal tabs, and roadmap.

next

Planned HTTP 402 response parser planned

Real endpoint probing and structured parsing of x402 payment requirement payloads — Phase 3 research.

Roadmap

Roadmap Preview

Phase 1

Website, docs, terminal preview

Launch site, documentation, and interactive terminal UI preview. Current

Phase 2

Registry schema and x402 metadata

Public registry.json, API detail pages, structured metadata fields, and schema documentation. Completed

Phase 3

Real HTTP 402 parser research

Endpoint probing and structured parsing of x402 payment requirements. Planned

Phase 4

MCP-ready API metadata

Agent tool documentation and future MCP server compatibility research.

Phase 5

Public x402 API registry submission system

Backend for listing and reviewing x402-compatible API endpoints.

Phase 6

MPP / Tempo compatibility research

Track machine payment protocol models as future research — not live.

Phase 7

Real CLI package

Installable CLI tool — planned, not published yet.

Phase 8

Agent mode and automation support

Structured output for AI tools and automation pipelines.

View Full Roadmap