json schema generator

runs in your browser, nothing is uploaded

IDLE

stdin

stdout

Made by Maiyarasu S

Generate a JSON Schema from a sample document, as a starting point you then tighten by hand. It targets draft 2020-12 and is built in your browser.

What the schema describes

The generator walks your sample and records the type of every value: object, array, string, integer, number, boolean or null. Objects get properties, and a key goes into required when it appears in every copy of that object. Arrays get an items schema built from all of their elements.

When a value has more than one type across the sample, plain types become a list such as ["string", "null"], and any mix that includes an object or an array becomes anyOf. Integers and decimals are told apart, so 3 is an integer and 3.5 a number.

What to add yourself

A schema made from one sample can only describe what it has seen. It does not guess formats, enums, minimum or maximum values, patterns or lengths. Add those where your data has rules, and check that every required key really is required.

The schema appears as a tree you can fold, copy or save as a .schema.json file. To test it, open the validator and put the schema in tab b, or press “generate a schema from tab a” there.

Questions

Which draft does it use?

Draft 2020-12, declared in $schema. The keywords it writes mean the same in draft-07, so older tools can read it too.

Why is a key missing from required?

At least one object in your sample does not have it. If the key must always be present, add it to required by hand.

Will the schema reject unexpected keys?

No. It does not add additionalProperties: false, so extra keys pass until you add that rule.

Is my data uploaded?

No. The schema is generated in this page.

Related tools

help

QUERY (the prompt line)

Type a path or a filter after guest@json:~$. JSONPath and a jq-style subset both work, and the output shows only the result. Convert, copy and save then apply to that result.

$.users[0].nameone value by path. .users[0].name is the same thing
$["odd key"] $.ports[-1] $.ports[1:3]quoted keys, counting from the end, slices
$.users[*].name or .users[].nameevery item
$..namethat key at any depth
$.users[?(@.id > 1001 && @.sudo)]filter. Operators: == != < <= > >= && || !
.users[] | select(.sudo) | .namethe same idea in jq style, with pipes
.users | map(.name) | sortbuild a new list
[.users[] | select(.sudo)] | lengthcollect matches into an array, then count

Functions: length, keys, keys_unsorted, values, type, first, last, sort, sort_by(f), unique, reverse, flatten, add, min, max, to_entries, not, select(f), map(f), has(k), test(regex), contains(x), startswith(s), endswith(s).

TABS A AND B

stdin has two tabs. diff compares a with b by structure: key order is ignored, and an item inserted into an array counts once. validate checks tab a against the JSON Schema in tab b. Click any row in either list to open that spot in the tree.

REPAIR

When input is not valid JSON, the error view lists what auto-fix would change, line by line, before you apply it: comments, trailing or missing commas, single or smart quotes, bare keys, NaN and Infinity, hex and other number spellings, markdown code fences, JSONP wrappers, and input that was cut off. undo brings your original back.

VALUE HINTS

Links are clickable. Numbers that look like Unix times show the date. A badge after a string means it holds something: {…} JSON, jwt a token (decoded, never verified), b64 base64 text. Click the badge, or press Enter on the row, to expand it in place. A token pasted on its own, with or without Bearer in front, is offered as decode jwt instead of a parse error. Decoding never checks the signature.

KEYS

Ctrl+F or /search the output: the tree, or the text of minify, yaml, csv and ts. Enter next match, Shift+Enter previous. Write /pattern/ for a regular expression. In text output the keys and values buttons are off, and diff and validate switch to the tree
Alt+Qgo to the query prompt. Esc clears it
↑ ↓ ← →move in the tree. Left and right fold and unfold, with Shift they do the whole branch
Enter / Ctrl+C in the treefold or expand the row / copy the selected value
Ctrl+Enterformat stdin in place
Ctrl+Ssave the output as a file
Alt+C Alt+M Alt+S Alt+Fcopy, pretty or minify, sort keys, fold
Alt+1 Alt+2 Alt+Ttab a, tab b, next theme
Tab / Shift+Tab in stdinindent and outdent. Press Esc first to tab out of the box instead
Ctrl+Z / Ctrl+Shift+Z in stdinalso undo and redo format, auto-fix, load and clear

On a Mac, use Cmd for Ctrl and Option for Alt.

SAVED INPUT AND DISPLAY

Both tabs are kept in this browser between visits, however large. If the browser cannot keep an input, a note says so. The crt button turns scanlines and glow off. The page also drops them, and brightens dim text and borders, when your system asks for more contrast.

PRIVACY

Everything runs in this page, and the fonts are served with it. Nothing you paste is sent anywhere. A share link holds the compressed input inside the link itself, so anyone you send the link to can read it.

What you paste is also saved in this browser, so it is still here on your next visit. On a shared computer, or after pasting a secret, clear it. This removes both tabs and your settings from this browser.