"How to connect a backend project to MongoDB" matching MCP connectors:

Buy a $2 novelty digital rock over x402 (USDC on Base). Serves payment instructions only.

Abstraxn Agent Kit gives AI agents instant access to real-time Web3, blockchain, and market data with no signup or API key. Access blockchain tools, crypto, wallet, ENS, transaction simulation, and travel APIs through one MCP server, with paid calls settled directly from the user's crypto wallet via x402—without Abstraxn holding or custodizing funds.

Is a wallet frozen by Tether/Circle? Free freeze checks + full history, screening & KYT. 9 chains.

Teardrop is the native economic layer for AI agents, providing a robust suite of tools for multi-chain portfolio tracking, DeFi yield analysis, and gas estimation. It enables autonomous agents to securely find Web3 data and manage micro-payments on-chain with zero human intervention.

Pay-per-call safety checks for AI agents: screen a crypto address or URL before you transact.

Trade crypto perpetual futures and spot on Rubin, a self-custody decentralized exchange, from AI agents — place and manage orders and read order books, candles, positions, and balances.

Live AI agent contest platform on Solana mainnet. Compete in skill tournaments (ART, STORY, JOKE) for real USDC payouts via on-chain Anchor smart contract. Confidential-rubric LLM judging on four dimensions: originality, theme_alignment, execution, surprise. Engine never holds private keys — entries use a two-call co-sign handshake.

Free, keyless MCP server with 50 read-only blockchain tools for Bitcoin, Ethereum, and Mezo. No installation, no API key required -- just add the URL to your MCP client and start querying balances, transactions, blocks, ENS names, ERC-20 tokens, smart contracts, and more. Runs on Cloudflare's global edge network via Streamable HTTP. All tools are strictly read-only and stateless.

Free, keyless MCP server with 50 read-only blockchain tools for Bitcoin, Ethereum, and Mezo. No installation, no API key required -- just add the URL to your MCP client and start querying balances, transactions, blocks, ENS names, ERC-20 tokens, smart contracts, and more. Runs on Cloudflare's global edge network via Streamable HTTP. All tools are strictly read-only and stateless.

Verified ROKI Connect payments contract for coding agents: operations, schemas, validator.

Live Bitcoin market regime for agents: three independent sensors read on-chain, off-chain and absence data every 30s and reject almost everything — when they converge, you get a directional call with the evidence attached. Public track record your agent can audit in one call. MCP + REST + x402. Free tier, no card.

Monetization gateway for MCP servers. Agents call a tool, receive an x402 v2 payment challenge, sign a USDC transfer on Base, and get the result. Payment is verified before the tool runs and settled only after it returns, so failed calls are never charged. Discovery and tool listing are free.

Wallet-addressed mailbox + storage for agents: pay to send (x402), read free with your key.

54+ pay-per-use AI & data tools for agents, payable in USDC via x402 on Solana — no API keys, no subscriptions. AI image, video, music and voice generation (cheaper than official APIs), web search, cited research reports, Claude Opus Q&A, crypto prices, page scraping, domain info and more. Pay only for what you call, straight from the agent wallet. Free directory tool lists all live endpoints.

PayRam is a self-hosted crypto payment gateway. You deploy it on your own server — no signup, no KYC, no third-party custody. Accept USDT, USDC, Bitcoin, and ETH across Ethereum, Base, Polygon, and Tron.

Stress-test lowcap, perp and LP strategies. Returns the full distribution and a reproduction seed.

Prediction-market fee/KYC/withdrawal data, venue recommendations, and a paid x402 change feed.

MCP marketplace: agents pay per call in USDC via x402. Plus Base chain data and a USDC<->bank ramp.

Verified dev-error fixes sold per-lookup to AI agents on-chain. Free search; 3 free samples.

Graded trading signals and market analysis for FX, crypto, sports, and prediction markets, with a public machine-graded track record. Free track-record and quote tools; paid tools via API key or per-call x402 USDC