Best LLM for JSON / Structured Output
Ranked on JSON-mode reliability, schema-adherence, and price. Failures here tax the rest of your pipeline.
Updated April 2026. Top 3 this month: GPT-5, Gemini 2 Pro, Claude Opus 4.7.
How we rank
Structured outputs — JSON, XML, YAML — look simple and are not. Models that are strong at prose can still fail to emit valid JSON under pressure. We weight JSON-mode support and schema adherence, then price; for agentic pipelines JSON reliability is often a bigger efficiency lever than raw reasoning.
Pillars and weights: JSON mode (50%) · schema adherence (30%) · price (20%). Our full methodology is published on the methodology page.
Top ranked models
| Rank | Model | Provider | Input $/1M | Output $/1M | Context |
|---|---|---|---|---|---|
| 1 | GPT-5 | OpenAI | $1.25 | $10.00 | 200,000 |
| 2 | Gemini 2 Pro | $3.50 | $10.50 | 2,000,000 | |
| 3 | Claude Opus 4.7 | Anthropic | $5.00 | $25.00 | 200,000 |
| 4 | GPT-5 nano | OpenAI | $0.05 | $0.40 | 400,000 |
| 5 | GPT-4.1 nano | OpenAI | $0.10 | $0.40 | 1,000,000 |
| 6 | GPT-4o mini | OpenAI | $0.15 | $0.60 | 128,000 |
| 7 | GPT-4.1 mini | OpenAI | $0.40 | $1.60 | 1,000,000 |
| 8 | o4-mini | OpenAI | $0.40 | $1.60 | 200,000 |
| 9 | GPT-3.5 Turbo | OpenAI | $0.50 | $1.50 | 16,385 |
| 10 | GPT-5 mini | OpenAI | $0.25 | $2.00 | 400,000 |
Tips for json / structured output
- Always send a schema. Most modern models support a constrained output mode.
- Validate server-side. Never trust the model to handle `null` vs. `undefined` correctly.
- If you see repeated schema violations, switch to function-calling rather than free-form JSON.
Frequently asked questions
Which LLM produces the most reliable JSON?
As of April 2026, our weighted top 3 are GPT-5, Gemini 2 Pro, Claude Opus 4.7.
JSON mode vs function calling?
Function calling is stricter and preferred for agent tools. JSON mode is fine for single-shot extraction.
Should I include a schema in the prompt?
Yes — even if your provider supports constrained decoding, an in-prompt schema reduces post-generation errors.
Related tasks
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Data refreshed daily via our snapshot cron. See our public JSON API for programmatic access.