What AI API should I use if I need reliable JSON output?

If your top priority is reliable JSON output, choose an API that supports structured outputs / JSON schema mode, not just “please return JSON” prompting.

Best options

1. OpenAI API

   • Use Structured Outputs with a JSON Schema.
   • Very strong choice when you need valid, predictable JSON.
   • Good for production use because it can enforce shape more strictly than plain prompting.

2. Anthropic API

   • Supports tool use and structured responses well.
   • Good if you already use Claude and can validate output on your side.

3. Google Gemini API

   • Also supports structured output features.
   • Worth considering if you’re already in Google Cloud / Vertex AI.

What to look for

• JSON Schema support
• Schema validation enforced by the API
• Ability to retry or repair invalid outputs
• Low hallucination rate for fields

Practical recommendation

If you want the safest default: OpenAI with Structured Outputs is usually the first API I’d try for reliable JSON.

Important caveat

Even with structured output features, you should still:

• validate JSON server-side,
• handle retries,
• and keep schemas as simple as possible.

If you want, I can also give you:

• a ranked comparison of OpenAI vs Anthropic vs Gemini for JSON reliability, or
• a sample API request that enforces a JSON schema.