What is JSON Schema and why generate one?

JSON Schema is a vocabulary for describing the shape of JSON data: which keys exist, what type each holds, and which are required. It powers validation (ajv, OpenAPI), editor autocomplete and API docs. Writing one by hand is tedious, so this tool reads a real sample like {"id":1,"name":"Lei"} and emits the matching schema with id typed as integer and name as string, so you start from working output instead of a blank file.

How does it infer the schema from a sample?

It parses your JSON, then walks the value recursively. Objects become type object with a properties map, arrays become type array with a merged items schema, and each leaf becomes its JSON Schema type. For example [1,2,3] yields items of type integer, while {"a":true} yields a property a of type boolean. The structure of your sample is mirrored one to one, so a three-level nested object produces a three-level nested schema.

How are required fields decided?

By default every key present in an object is listed in that object's required array, because the safest assumption from a single sample is that all observed keys are mandatory. Toggle Add required off and no required arrays are emitted, leaving every field optional. For real data with optional fields, feed a representative sample or relax the list afterward, since one sample cannot tell which keys are optional.

What happens with a mixed-type array?

When an array holds elements of different types, like [1,"two",true], a single items type would be wrong. The tool emits items as an anyOf listing each distinct element schema, so {"anyOf":[{"type":"integer"}, {"type":"string"},{"type":"boolean"}]} keeps every observed element valid. Homogeneous arrays such as [1,2,3] collapse to one items schema instead, and an empty array leaves items open.

What is the difference between draft-07 and 2020-12?

They are two versions of the JSON Schema spec. The main thing this tool changes between them is the $schema URL it stamps at the top: http://json-schema.org/draft-07/schema# for draft-07 versus https://json-schema.org/draft/2020-12/schema for 2020-12. Pick the one your validator targets. The property, type, required and anyOf keywords used here are valid in both drafts, so the body is portable.

Does my JSON get uploaded anywhere?

No. Everything runs client-side with JSON.parse and a small amount of JavaScript. Open DevTools, Network panel while you generate and you will see zero requests carrying your data. The only way a sample leaves your machine is if you share the URL, which encodes the input; for sensitive payloads, copy the schema text instead of sharing the link.

Bootstrap a request-body schema for API docs

You already have a working JSON response from your endpoint but no OpenAPI schema written for it. Paste one real sample, get a draft-07 schema with every field typed and listed in required, then paste that into your spec under components/schemas. Five seconds replaces ten minutes of hand-typing braces, and the types match the data exactly because they were read off the data, not guessed.

Add validation to a config file you inherited

A legacy service reads a settings.json with thirty keys and zero guardrails. Drop one valid config in, generate the schema, wire it into ajv or a CI check, and now a typo in a boolean flag fails the build instead of crashing in production at 3 am. The required toggle lets you mark every key mandatory or leave them optional in one click.

Catch a shape change in a third-party webhook

Stripe or GitHub ships a webhook payload and you want to freeze its shape. Generate a schema from today's sample, commit it, and the next time the provider sneaks in a renamed field your validator flags the drift before it reaches your handler. Switch to 2020-12 if your validator targets the newer draft.

Teach JSON Schema by example in a workshop

Explaining anyOf and required to a class is easier when learners can paste their own JSON and watch the schema appear. Mixed-type arrays turn into anyOf in front of them, integers separate from numbers, and the draft toggle shows how the $schema line changes between versions without anyone touching a single brace by hand.

JSON Schema Generator, Infer a Schema From Any JSON Sample

Paste a JSON sample, get a typed JSON Schema (draft-07 or 2020-12) in your browser

Runs locally
Category Developer & DevOps
Best for Formatting, validating, shrinking, or inspecting code-adjacent text.

Draft:

Add requiredAdd examples

JSON sample

JSON Schema

Enter a JSON sample, then click Generate Schema.

What this tool does

Generate a JSON Schema from a JSON sample, instantly and entirely in your browser. Paste one real object or array and the tool walks it recursively, typing every value as string, number, integer, boolean, null, object or array, building object properties with a required list you can switch on or off, and collapsing array elements into a single item schema (or anyOf when the array mixes types). Pick draft-07 or 2020-12 and the $schema line updates to match. Turn on examples to embed your original sample for documentation. Output is pretty-printed and one click from your clipboard. No upload, no account, no waiting on a server. This is the fast path from a payload you already have to a schema you can drop into OpenAPI, ajv, a CI validation gate or your editor settings.

Tool details

Input: Text + Structured content; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 10 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Developer & DevOps · Developer; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How JSON Schema Generator fits into your work

Use it in the small gaps between coding, reviewing, debugging, and shipping.

Developer jobs

Formatting, validating, shrinking, or inspecting code-adjacent text.
Preparing snippets for documentation, tickets, commits, or handoff.
Checking a small payload quickly without switching tools.

Developer checks

Run irreversible transforms like minify or obfuscate on a copy.
Keep secrets out of pasted snippets unless the tool explicitly stays local.
Use your normal tests or linter before shipping transformed code.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Bootstrap a request-body schema for API docs
You already have a working JSON response from your endpoint but no OpenAPI schema written for it. Paste one real sample, get a draft-07 schema with every field typed and listed in required, then paste that into your spec under components/schemas. Five seconds replaces ten minutes of hand-typing braces, and the types match the data exactly because they were read off the data, not guessed.
Add validation to a config file you inherited
A legacy service reads a settings.json with thirty keys and zero guardrails. Drop one valid config in, generate the schema, wire it into ajv or a CI check, and now a typo in a boolean flag fails the build instead of crashing in production at 3 am. The required toggle lets you mark every key mandatory or leave them optional in one click.
Catch a shape change in a third-party webhook
Stripe or GitHub ships a webhook payload and you want to freeze its shape. Generate a schema from today's sample, commit it, and the next time the provider sneaks in a renamed field your validator flags the drift before it reaches your handler. Switch to 2020-12 if your validator targets the newer draft.
Teach JSON Schema by example in a workshop
Explaining anyOf and required to a class is easier when learners can paste their own JSON and watch the schema appear. Mixed-type arrays turn into anyOf in front of them, integers separate from numbers, and the draft toggle shows how the $schema line changes between versions without anyone touching a single brace by hand.

Common pitfalls

Treating one sample as the whole truth. A schema inferred from a single object only knows the keys that sample had. If other records carry an optional field your sample lacked, the generated required list will be too strict. Feed a representative array, or relax required afterward.
Expecting formats like date-time, email or uuid to be detected. This tool infers structural types (string, integer, object, array), not semantic string formats. A timestamp string comes out as type string. Add format keywords by hand where your validator needs them.
Forgetting that integer and number are different. A sample value of 10 infers integer, so 10.5 would fail that schema. If a field can hold decimals, make sure your sample actually shows a decimal, or widen the type to number yourself.

Privacy

Inference runs entirely in your browser with JSON.parse and a few lines of plain JavaScript. The sample you paste, the generated schema and every option you toggle stay inside the tab; nothing is uploaded and nothing is logged. One caveat: the shareable URL encodes your input in the query string, so a link pasted into chat records that sample in the recipient server access log. For a confidential payload, use the copy button on the schema instead of sharing the URL.

FAQ

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JSON Schema Generator, Infer a Schema From Any JSON Sample

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How JSON Schema Generator fits into your work

Developer jobs

Developer checks

Good next steps

Real-world use cases

Bootstrap a request-body schema for API docs

Add validation to a config file you inherited

Catch a shape change in a third-party webhook

Teach JSON Schema by example in a workshop

Common pitfalls

Privacy

FAQ

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