APIStack

APIStack is an API and Model Context Protocol service providing deterministic tools, validation checks, and REST endpoints for AI agents.

APIStack equips AI agents like Claude, ChatGPT, and Cursor with deterministic tools and utilities via Model Context Protocol servers and REST APIs. It handles tasks agents should not answer from memory, such as currency conversion, holiday calendars, date arithmetic, IBAN and VAT validation, and sanctions checks. Agents can connect through dedicated servers or a unified MCP endpoint that uses three tools to search and execute catalog APIs without consuming heavy context. It is built for developers creating agentic workflows in IDEs and custom applications. Users can filter tools by categories or specific APIs directly in the endpoint URL.

APIStack at a glance

Best for: Software engineer
Runs on: Web, API, VS Code
Pricing: Free plan includes 1,000 calls/month; Pro costs $19.99/month for 100,000 calls; Enterprise costs $79.99/month for 1,000,000 calls.
Released: October 2026
Category: AI agent tool
Website: apistack.online

Key features

Connect AI agents to tools using a single unified MCP endpoint
Screen entities against sanctions lists
Validate VAT numbers, IBANs, email addresses, and phone numbers
Calculate dates, working days, and shared meeting hours across time zones
Convert currencies and fetch economic indicators for countries
Check URLs for safety risks
Filter available tools directly via endpoint URL query parameters

Use it for

Equipping coding assistants in Cursor or VS Code with live utility tools
Validating payment, VAT, and customer contact data inside automated workflows
Calculating business days and cross-time-zone meeting availability for AI assistants
Running automated compliance and sanctions screening within agent prompts

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