Free JSON Validator with Side-by-Side Diff (Browser-Only)

What is a JSON validator?

A JSON validator parses a string of text against the JSON specification (RFC 8259) and tells you whether it's syntactically correct. Strict validators only accept exactly what the spec allows: double-quoted keys and strings, no trailing commas, no comments, no Date objects, no NaN. Lenient (or 'JSON5-ish') validators relax those rules to fix the kinds of malformed JSON you actually encounter — config files, log payloads, hand-edited fixtures.

A JSON diff tool — sometimes called a JSON compare or JSON merge tool — goes one step further: it parses two JSON documents and reports the structural differences between them, by path. Line-by-line text diffs are noisy for JSON because reformatting, key order, or one extra indent generates dozens of red and green lines for a single logical change. Semantic diff compares parsed structures, so the output is a clean list of additions, removals, and value changes — independent of formatting.

When the diff is between two states of the same document (an old API response vs a new one), you can serialize that diff as JSON Patch (RFC 6902) — an IETF-standard array of add / remove / replace operations with JSON Pointer paths. PATCH endpoints, version-control systems, and migration tools consume RFC 6902 directly, so you can copy the patch from a diff tool and apply it programmatically.

What this tool does

Strict and lenient JSON parsing

Strict mode runs native JSON.parse and reports the offending line and column. Lenient mode auto-fixes trailing commas, single quotes, JS-style comments, and unquoted keys — and tells you what was fixed.

Format / beautify / minify

Pretty-print with configurable indent (2 / 4 / tab), sort keys alphabetically, or minify to a single line. All in-browser, all instant.

Side-by-side semantic diff

Two aligned panes color-code added / removed / changed values, aligned by JSON path. Hide identical hunks, follow path breadcrumbs as you scroll, character-level highlight on changed strings.

JSON Schema (Draft 7 subset) validation

Validate any payload against a Schema with type, required, properties, items, enum, min/max, length, pattern, oneOf, anyOf — error reports include the offending JSON path.

RFC 6902 JSON Patch export

Copy the structural diff as a standard JSON Patch operation array — drop it directly into a PATCH endpoint or any RFC 6902 library.

JSON-LD (Schema.org) detection

Recognises Schema.org JSON-LD blocks via @context and links to our LocalBusiness markup generator if you need help building them correctly.

Privacy-first: nothing leaves your browser

All parsing, formatting, and diffing run inside your tab. No upload, no server logs, no tracking pixel, no rate limit. You can disconnect from the internet and the tool keeps working.

No size limit

There's no enforced cap on input. Practical ceiling is your browser's memory budget (typically a few hundred MB) — large logs and dump files parse fine.

How it works

Three steps, no account needed.

Validate or format JSON

Paste any JSON in the Validate tab. Strict mode flags syntax errors with line and column. Lenient mode auto-fixes trailing commas, single quotes, JS-style comments, and unquoted keys, and reports each fix.

Compare two JSON payloads side by side

Switch to the Compare tab and paste a second JSON. Two aligned panes color-code added, removed, and changed values. Hide identical lines, sort keys, and follow the path breadcrumb as you scroll.

Validate JSON Schema or detect JSON-LD

Paste a Draft 7 schema to validate your data against it. Schema.org JSON-LD blocks are auto-detected with a one-click jump to our Schema Markup Generator. Export the diff as RFC 6902 JSON Patch.

Why use this tool

Built for developers who debug JSON every day.

Free JSON validator with no signupMost online JSON validators require an account or upload your data. This one runs entirely in your browser. No tracking pixel, no rate limits, no server traffic.

Side-by-side JSON diff that aligns by pathBoth panes line up on the same key in the same row, even when one side has extra fields. Hide-identical collapses unchanged hunks. Inline character-level highlight on changed strings.

Lenient mode for real-world JSONCatches trailing commas, JS-style comments, single quotes, and bare keys — the exact bugs you paste from logs and config files. Each fix is reported so you can patch the source.

JSON Schema (Draft 7 subset) validatorValidate any payload against a Schema with type, required, properties, items, enum, min/max, length, pattern, oneOf, and anyOf checks. Errors include the offending path.

RFC 6902 JSON Patch exportCopy the diff as a standard JSON Patch operation array. Drop it straight into a PATCH endpoint, into a JSON Patch library, or into a code review.

JSON-LD awareDetects Schema.org JSON-LD blocks (@context: "https://schema.org") and offers a one-click jump to our free Schema Markup Generator that builds LocalBusiness markup from your verified Google Business Profile.

Who this tool is for

JSON shows up everywhere — APIs, config files, log payloads, structured data. Three audiences pull the same validator for different reasons.

Backend and frontend developers

You debug JSON every day — API responses that don't match the schema, config files with stray commas, two payloads that should be identical and aren't. A validator that handles real-world malformed JSON and a path-aware diff are faster than reaching for jq + git diff every time.

DevOps and SRE

You compare config snapshots between environments, validate IaC outputs against schemas, and ship JSON Patch operations to running services. RFC 6902 export turns a local diff into something you can apply via a PATCH endpoint or store as an audit trail.

Technical SEOs and structured-data engineers

JSON-LD is what powers rich results. Validating Schema.org blocks before they ship and diffing two versions of a page's structured data catches subtle breaks — a missing @type, a swapped @id, a renamed property — that Search Console won't surface for weeks.

How this validator compares

Most online JSON tools either upload your data or hide the diff behind an account. This one runs entirely in your browser and exposes every feature on the free tier.

What you'd want	This tool	Most online JSON tools
Where parsing happens	100% in your browser	Many upload your JSON to a server
Account or signup	None — open the tab and use it	Often required for diff or schema validation
Lenient parsing for real-world JSON	Yes — trailing commas, single quotes, comments, bare keys auto-fixed	Strict-only validators fail on common log/config formats
Side-by-side semantic diff	Aligned by JSON path, hide identical, character highlight	Many do line-by-line diffs that are noisy for JSON
RFC 6902 JSON Patch export	Yes — one click, ready for PATCH endpoints	Rarely available outside paid tooling
JSON Schema validation	Draft 7 subset on the free tier	Frequently a paid feature

Frequently asked questions

Is this JSON validator free?

Yes — completely free, no signup, no rate limits. Validation, formatting, and comparison all run inside your browser using JavaScript. There is no premium tier and no upsell.

How do I validate JSON online?

Paste your JSON into the Validate tab. The tool runs the native JSON parser and reports the exact line and column of any error. Switch to lenient mode to also accept trailing commas, single quotes, JS-style comments, and unquoted keys.

How do I compare two JSON files?

Open the Compare tab and paste each JSON into the left and right panes. The side-by-side view highlights additions in green, removals in red, and value changes in yellow, all aligned by key path. Toggle Hide identical to skip unchanged sections.

Is online JSON validation safe and private?

Yes. All parsing, formatting, and diffing run inside your browser tab. Nothing is sent to a server, nothing is logged, nothing is cached on disk by us. You can disconnect from the internet and the tool keeps working.

What is the difference between strict and lenient JSON parsing?

Strict mode uses the native JSON.parse and follows the JSON spec exactly. Lenient mode applies a series of fixes — strips line and block comments, converts single quotes to double, quotes bare keys, and removes trailing commas — then parses the result and reports each fix that was applied.

Why does my JSON say invalid?

The most common causes are trailing commas after the last item in an object or array, single-quoted strings, unquoted property names, and JS-style // or /* */ comments. The JSON spec doesn't allow any of these. Switch to lenient mode to auto-fix and see exactly what was wrong.

What is a JSON path?

A dot- and bracket-notation address for a value inside a JSON document. For example, users.0.email means the email field of the first item in the users array. The compare view tags every change with its path so you know exactly where in the structure something differs.

Why use semantic diff instead of line-by-line?

Line diffs are noisy: reformatting, sort order, or an extra indent generates dozens of red and green lines for one logical change. Semantic diff compares the parsed structures and reports changes by path, so you get a clean list of what actually changed in the data — independent of formatting.

What JSON Schema features are supported?

A Draft 7 subset: type, required, properties, items, enum, minimum, maximum, minLength, maxLength, pattern, oneOf, and anyOf. Full Draft 7 or 2020-12 features like $ref, $defs, if/then/else, unevaluatedProperties, and format are not supported in this tool.

What is JSON-LD and why does it matter for SEO?

JSON-LD is a way to embed Schema.org structured data inside a web page so search engines understand what the page is about. Google uses it to power rich results — star ratings, breadcrumbs, FAQ accordions, local business panels. Getting the syntax right matters, which is why the validator flags JSON-LD blocks and links to a generator that builds them correctly.

What is JSON Patch (RFC 6902)?

JSON Patch is the IETF standard format for expressing changes to a JSON document as a list of operations: add, remove, or replace, each with a JSON Pointer path. Backend APIs use it for PATCH endpoints that accept granular updates instead of a full body replacement. Copy the patch from the Compare tab and apply it with any RFC 6902 library.

What does Sort keys do?

When Sort keys is on, all object keys are sorted alphabetically before output. This applies to the formatted output in the Validate tab and to both panes in the side-by-side compare view. Useful when comparing two payloads that have the same keys in different orders — without sort, key order changes show as no-op diffs.

What does Hide identical do?

When on, runs of three or more identical lines collapse into a single click-to-expand row. This lets you focus on the differences without scrolling past unchanged sections. One context line on each side of every change is always kept visible, so you don't lose your place.

Is there a maximum input size?

No hard limit is enforced by the tool. Very large JSON (tens of megabytes) may briefly pause the browser tab while parsing and rendering, but the practical ceiling is your browser's memory budget — typically a few hundred MB.

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The free JSON validator