"A search for engineering textbooks with charts, formulas, and graphs" matching MCP servers:

Pay-per-use semantic web search for AI agents. Powered by SearxNG, agents pay in sats via Lightning Network micropayments — no API keys required.

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

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.

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.

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.

Enables MCP-capable agents to search the curated gold-402 directory of x402 services, probe any endpoint for valid 402 payment terms, and optionally purchase a human editorial verdict for a resource.

Discover and pay for APIs and MCP tools per call over Bitcoin Lightning (L402): search the bolthub marketplace, preview prices, and pay from your own wallet (LND, NWC, LNbits) with hard budgets, prepaid credit, scoped sub-agent delegation, and verifiable receipts. Non-custodial and works without a wallet for search and free tools.

MCP server for Brazilian marketplace product search across Mercado Livre, Shopee, and AliExpress, with automatic x402 micropayments.

Enables Claude to interact with a Folio business bank account for managing accounts, transactions, receipts, bookkeeping, and payments as drafts.

A single MCP gateway for Allternit LLC business operations, providing tools for Stripe invoicing, Cloudflare Pages deployment, brain document search, and client folder creation, all with safety confirmations for destructive actions.

Enables AI agents to search, license, and pay for rights-clean music per use, returning a verifiable license certificate.

Enables AI assistants to search for and purchase gift cards, mobile topups, and digital products via Bitrefill, with tools for managing invoices, orders, and account balance.

Enables interaction with Safaricom M-Pesa Daraja 3.0 API, covering payments, disbursements, treasury, and fraud checks, with a built-in simulator for testing without credentials.

An MCP server for Danish accounting via Billy.dk API, enabling natural-language control over invoices, bank lines, reports, and more, with a write-guard for safety.

An MCP server that enables AI agents to search, pay for, and call paid APIs using the x402 protocol, with automatic USDC settlement.

Reference MCP server for K-product cross-border commerce with five canonical tools for product search, cart creation, checkout quoting, and order submission.

MCP Server for agents to onboard, pay, and provision services autonomously with InFlow

MCP server that allows AI agents to discover and pay for thousands of APIs (x402 on Solana/Base) using a single key, with automatic payment handling and a federated catalog of machine-payable endpoints.

Enables AI agents to discover and interact with a merchant's commerce layer, including product listing and checkout creation, while payments settle directly to the merchant's Stripe account.