Infer a Draft JSON Schema from a Local Sample

How to Use This Tool

Create a deterministic first-draft schema without sending sample payloads to a model. Infer JSON Schema 2020-12 types, object properties, required keys and array item shapes from pasted sample JSON, with local parsing and download.

The work this page finishes

API samples often contain private or pre-release fields, and manually writing nested type scaffolding creates omissions before meaningful constraints are even discussed. Keeping source order beside the computed artifact lets a user repair only the failed entries and reproduce the same batch later.

Deterministic workflow

Parse the exact JSON locally, infer primitive types recursively, merge differing array item types and optionally mark keys observed in each object as required. A run is capped at 5,000 items and 2 MB, preventing an accidental oversized paste while preserving successful rows when another row fails.

Why a dedicated interface helps

Treat the result as a first draft: review optionality, formats, enums, numeric bounds, additionalProperties and cross-sample variation before validation use. A purpose-built form exposes every assumption and returns the same ordered structure on every run, which is more practical than reconciling shifting conversational output.

Assumptions

• The sample is valid JSON rather than JavaScript.
• Observed primitive types are representative.
• Required-key inference is explicitly user controlled.

Keep an untouched copy for comparison after import; the browser performs the work locally, but local software and extensions are not controlled by this page.

Limitations and review boundary

One sample cannot prove optional fields or all allowed values, and mixed object shapes are conservatively reduced rather than synthesized into a complete domain contract. The implementation neither follows user-entered links nor evaluates their contents, and it displays material as plain text rather than active HTML.

Verification and provenance

Fixtures derived from the displayed rule and JSON Schema 2020-12 specification were reviewed on 2026-08-26; they include normal, empty or invalid, and partial-failure behavior. The default object yields four required properties and an array of string items under Draft 2020-12.