Agent Tools APIs let you add agent tools-powered 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 | |
| DELTA Witness Browser verification and page-state proof for public sources, plus deterministic preflight checks before an autonomous action. DELTA proves observation and change, not truth. | Paid | No | Yes | Profile | |
| Dust API Team AI agents over company data, controllable via API. | Unknown | Unknown | Yes | Profile | |
| Gumloop API AI-native automation platform to build and run agent pipelines. | Unknown | Unknown | Yes | Profile | |
| Letta API Stateful agent API for memory, tools, conversations, and agent orchestration. | Freemium | API Key | Yes | Profile | |
| Mastra Cloud API TypeScript agent framework with hosted deployment and APIs. | Unknown | Unknown | Yes | Profile | |
| Mistral Agents API Agent API for Mistral models with tools, connectors, and orchestration. | Freemium | API Key | Yes | Profile | |
| Relevance AI API No-code agent builder with APIs to run AI agents and tools. | Unknown | Unknown | Yes | Profile | |
| Retell AI API Build production voice agents with low-latency speech APIs. | Unknown | Unknown | Yes | Profile | |
| Smithery API Registry and gateway to discover, install and run MCP servers. | Unknown | Unknown | Yes | Profile | |
| SmythOS API Orchestrate, deploy and manage autonomous AI agents. | Unknown | Unknown | Yes | Profile | |
| Vapi API Voice AI agent API for phone calls, assistants, tools, and workflows. | Freemium | API Key | Yes | Profile | |
| Vellum API Develop, evaluate and deploy AI workflows and agents. | Unknown | Unknown | Yes | Profile | |
| n8n API Workflow automation with AI-agent nodes; scriptable via public API. | Unknown | Unknown | 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 agent tools 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.