Feature
Function Calling & Tool Use
Structured tool definitions LLMs can invoke.
19 providers
104 APIs
18 declared variants
Capabilities are exposed as tool or function definitions an LLM can call with structured arguments. The mechanism behind most agentic integrations today.
19 API providers on the APIs.io network offer function calling & tool use. The highest-rated are OpenAI, Anthropic, Vapi, NVIDIA NIM, Hyperbolic.
Providers
Ranked by API Evangelist rating — Exemplar and Strong are expanded by default.
Exemplar 4 Complete, well-documented, and agent-ready
OpenAIOpenAI publishes a single unversioned REST API at https://api.openai.com/v1 covering text and reasoning (Re...AnthropicAnthropic is an AI safety company and the creator of the Claude family of large language models (Opus, Sonn...VapiVapi is a San Francisco-based voice AI platform that lets developers build real-time, low-latency voice age...NVIDIA NIMNVIDIA NIM (NVIDIA Inference Microservices) is a catalog of GPU-accelerated, containerized AI inference mic...
Strong 6 Solid coverage with minor gaps
HyperbolicHyperbolic is an open-access AI cloud and decentralized GPU marketplace serving 200,000+ builders with affo...ExaExa is a web search API and AI research platform built specifically for LLMs and agents — semantic and keyw...LakeraLakera is an AI-native security platform that protects GenAI applications, agents, and workforces from prom...Arcade.devArcade.dev (formerly Arcade AI) is the MCP runtime for production AI agents — a platform that lets agents s...PerplexityPerplexity AI is an answer engine that delivers accurate answers to complex questions using large language ...ClaudeAnthropic's Claude AI assistant API for natural language processing and conversation.
Developing 5 Usable, with meaningful gaps to close
Mistral AIMistral AI provides state-of-the-art large language models and AI APIs for developers and enterprises.Lunar EnergyLunar Energy is a Mountain View, California-based residential clean-energy company founded in August 2020 b...OpenRouterOpenRouter is an API platform that provides unified access to multiple AI language models through a single ...GeminiGoogle's Gemini API provides access to state-of-the-art generative AI models for text generation, multimoda...DoclingDocling is an open-source toolkit for parsing diverse document formats — PDF, DOCX, PPTX, XLSX, HTML, image...
Thin 3 Limited public surface area
cohereGenerates a text response to a user message and streams it down, token by token.Agent SkillsA collection of resources, APIs, and standards related to AI agent skills and capabilities. Agent skills re...CrestaCresta (legally Cresta Intelligence, Inc.) is a Palo Alto, California enterprise Customer Experience AI com...
Minimal 1 Almost no public developer surface
What Providers Actually Declared
This feature is a canonical term. These are the free-text strings
providers wrote in their own apis.yml that map onto it.
AI Agent Security — runtime protection for autonomous agents and tool useAI Agent consumes external tools via API function calling and MCP (Cresta is an MCP client, not an MCP server)Function CallingFunction calling and tool useFunction calling, JSON mode, tool use, and structured outputs across compatible LLMsMCP runtime engine for secure, multi-user AI agent tool callingMCP server (docling-mcp) exposes parsing as agent tools for Claude, Cursor, Gemini and other clientsMessages API with text, vision, tool use, extended thinking, streaming, structured outputsRemote MCP server exposes the Customer API as agent toolsStreaming, tool/function calling, structured JSON output, vision input on supported modelsStructured Outputs for JSON-schema-constrained extraction from callsStructured output (JSON schema)Structured outputs with web-grounded citationsTool UseTool use / function calling (model-dependent)Tool use and function callingTravel Agent ToolsVision, tool use, structured outputs, and function calling
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Work with this as data
Every feature here is available over the APIs.io API and to AI agents over MCP. Features is not yet its own endpoint on the v1 API. Reach it through catalog search and the tag graph, or the MCP server.