"Guidance on Writing Software" matching MCP servers:

Enables AI agents to call paid APIs and settle HTTP 402 payment challenges with USDC on Base, without private keys ever being involved.

Pay-per-call USDC payment proxy for AI agents. Issue scoped Pay Tokens with hard spending caps and auto-journal every charge to freee / Money Forward / QuickBooks.

Lets an AI agent hire and pay a verified human: post real-world tasks (voice, observation, judgment) and pay in USDC via a non-custodial x402 auth-capture escrow on Base, budget frozen at deploy. Humans verify their X identity before submitting.

MCP server that lets a chatbot browse eSIM plans, sign in, prepare quotes, and execute wallet or card purchases on an existing eSIM platform, with safe typed tools.

Provides a non-custodial USDC wallet on Base for AI agents, with human-in-the-loop approval for every payment.

Enables AI coding assistants to log billable hours into the Keeping time-tracking service via MCP tools, with dry-run protection for all write operations.

Enables AI agents to call LLM APIs via x402 micropayments in USDC on Base network, manage a local wallet, and query consumption records.

MCP server providing Polymarket weather-market bucket-transition signals for AI agents, with free city/signal inspection tools and paid signal bundles via USDC on Base using x402.

Enables running a local MCP server for Poland's KSeF (Krajowy System e-Faktur) e-invoicing system, so invoice data stays on the user's own machine rather than passing through an intermediary service. It currently exposes only a diagnostic server_info tool, with invoice search and retrieval tools still to come.

MCP server for real FDM 3D-printing slicing, quoting, and design-for-manufacturability analysis via the FabTally API, supporting 12 printer profiles and 12 materials. Includes free discovery/printability tools and paid slice/quote/orientation tools settled via x402 (USDC on Base).

Enables MCP clients to access all endpoints of an x402 gateway by paying real-time microtransactions (USDC on Base) per API call, with automatic tool discovery and spend guardrails.

Enables AI agents to discover, inspect, and pay for paid HTTP and MCP services using USDC on Solana with a self-custodial wallet.

Provides AI agents with SSRF-protected URL intelligence and 32 paid REST/MCP tools, plus a free catalog search, with payments in USDC on Base Mainnet.

Unofficial MCP server for Oblio.eu accounting software enabling natural language interaction to create invoices, manage documents, collect payments, query nomenclatures, and submit e-Factura to Romania's SPV system.

minia2a.uk is a marketplace where AI agents buy and sell services from each other. Built on the x402 protocol (HTTP 402 Payment Required), every API call includes automatic USDC micropayment — no subscriptions, no API keys, no monthly bills.

Enables AI agents to post tasks, manage escrow, approve work, and pay human gig workers on the GetterDone physical-task marketplace.

Payment firewall for AI agents: a signed, independently verifiable verdict on every money-moving action. Blocks wrong/lookalike payee, over-cap, and duplicate-invoice (BEC) fraud before money moves — anyone can verify a verdict against the public JWKS. Free, local-first, non-custodial.

Enables issuing invoices, proformas, and delivery notices, collecting payments, submitting e-Factura to Romania's SPV, and querying reference data on Oblio.eu through natural language from MCP clients.

Payment infrastructure MCP server enabling AI agents to make gasless USDC payments on Base and JIT single-use virtual card checkouts, with zero-trust card handling, merchant checkout hints, and signed receipts.

Provides access to 70 paid APIs as MCP tools with per-call and session budgets, paying via x402/USDC on Base without requiring an account or login. Includes a built-in allowlist of hosts and safe defaults to prevent unintended payments.