What LLM API should I use for reliable tool use?

If your main goal is reliable tool use—meaning the model consistently picks the right tool, fills arguments correctly, and doesn’t drift—you generally want an API/model stack that supports:

• Structured outputs / function calling
• Low hallucination rate
• Good instruction-following
• Streaming + retries / validation on your side

Best general-purpose picks

1) OpenAI API

Best overall if you want strong, dependable tool calling and mature structured output support.

Why it’s a good choice:

• Very strong function calling / tool calling
• Good at following schemas and returning valid arguments
• Easy to build robust agents with JSON schema validation
• Broad ecosystem support

If reliability is your top priority, this is often the first choice.

2) Anthropic API

Also excellent for tool use, especially for more thoughtful reasoning and careful instruction following.

Why use it:

• Strong tool-use behavior
• Often very good at multi-step reasoning
• Good when you want conservative, well-structured responses

3) Google Gemini API

Can be good too, especially if you’re already in Google’s ecosystem, but in many agent/tooling setups it’s usually not the first recommendation for “most reliable” tool use compared with OpenAI/Anthropic.

Practical recommendation

If you want the shortest answer:

• Use OpenAI if you want the most straightforward and reliable tool-calling experience.
• Use Anthropic if your use case benefits from careful reasoning and you’re okay with a slightly different tool-use style.
• Add your own schema validation, retry logic, and fallback handling regardless of provider.

What matters more than the model alone

Even the best model benefits from a solid orchestration layer:

• Enforce JSON schema validation
• Reject/repair invalid tool arguments
• Use temperature = 0 or low temperature for deterministic behavior
• Keep tool descriptions short and unambiguous
• Break complex actions into smaller tools
• Add guardrails for tool selection

If you want a single recommendation

OpenAI API with structured outputs/function calling is the safest default for reliable tool use.

If you want, I can also give you:

1. a head-to-head comparison of OpenAI vs Anthropic vs Gemini for tool use, or
2. a reference architecture for building a reliable tool-using agent.