Agent Tools APIs let you add agent tools capabilities without building from scratch. Every entry below is profiled with trust signals — pricing model, authentication requirements, CORS support, rate limits, and live uptime checks — so you can compare options and pick production-safe choices instead of guessing from a link list.
| API | Pricing | Auth | CORS | Health | |
|---|---|---|---|---|---|
| Bland AI API AI phone calling API for outbound and inbound voice agents. | Freemium | API Key | Yes | Profile | |
| Composio API Tool and integration API for AI agents to connect with SaaS apps and execute actions. | Freemium | API Key | Yes | Profile | |
| Letta API Stateful agent API for memory, tools, conversations, and agent orchestration. | Freemium | API Key | Yes | Profile | |
| Mistral Agents API Agent API for Mistral models with tools, connectors, and orchestration. | Freemium | API Key | Yes | Profile | |
| Vapi API Voice AI agent API for phone calls, assistants, tools, and workflows. | Freemium | API Key | Yes | Profile |
Start with pricing and auth: free tiers and no-auth APIs are fastest to prototype with. Then check CORS if your app calls the API from the browser, and health before you commit — a great API that's been down for a week will block your launch. Each profile below shows all of these signals plus rate limits where documented.