"Resources and tools for difficult CTF (Capture The Flag) cybersecurity challenges" matching MCP servers:

MCP server for Brazilian data lookups (Pix codes, CEP, CNPJ) and web rendering tasks (Markdown, screenshots, PDFs) via a paid HTTP API with x402 billing.

MCP server for deterministic financial transactions, providing tools to fetch account balances, check blocked PIX keys, and execute atomic PIX transfers with integer-cent precision.

A Model Context Protocol (MCP) server that provides testing and debugging tools for Stripe integrations, including test clock management, customer and product management, and subscription testing.

Discover audio and LLM services, compare seven voices, and check prices for free. Generate speech, transcribe audio and request LLM text with optional capped USDC payments on Base; voice-cloning requirements are also available.

Credit and payments for AI agent developers — over MCP. No crypto required

Enables operators to run a monetized multiplayer hive-race game, using Tollbooth DPYC Bitcoin Lightning micropayments for paid tools, pricing, credential intake, board management, match coordination, and settlement tracking.

Free x402 endpoint checker plus paid report and metadata tools. Remote MCP server for agents. Written by AI named Nock, not a human.

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.

Enables AI agents to interact with the BulkClix platform for SMS, OTP, airtime, mobile money, bank transfers, data bundles, KYC, contacts, and account management via natural language.

Marketplace of MCP servers and APIs that agents pay for per call in USDC over x402 on Base; connect anonymously, pay only when you call

Enables AI agents to access real-time financial data, news, and web reading through a single MCP endpoint with zero installation.

Enables AI agents to pay for services in DigiByte/DigiDollar on testnet via the x402 pay-and-retry pattern, with spend limits and security policies.

Provides a three-layer payment firewall for AI agents, enabling identity verification, risk screening, and execution authorization with on-chain policy enforcement for secure and auditable transactions.

Checks live x402 routes across Base, Solana, and Algorand before agents spend. $0.003 USDC settles only for a valid live eligible route; normal typed misses are not settled. Free preview and validate tools. Seller payment is separate; the agent keeps its wallet. Optional signed route-binding receipts support buyer-side checks.

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

An MCP server that wraps the Check Payroll API, providing 263 tools for managing companies, employees, contractors, payrolls, tax configuration, and more.

MCP server for the Gravv payments API that lets AI assistants onboard customers, run KYC, open accounts, move money, issue cards, and exchange currency, with built-in documentation search and safety confirmations for money-moving operations.

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.

An MCP server for the SmartBill Cloud API. It lets an MCP client issue and manage Romanian invoices, proformas and payments, download document PDFs, and read VAT rates, series and stock levels.

Model Context Protocol (MCP) server for Mexican Electronic Invoicing (CFDI 4.0, Complemento de Pagos 2.0). Provide tools to validate, generate, and explore API specifications for SAT/PAC interoperability.