What's the file size limit?

The API endpoint accepts up to 1 MB of JSON per request. For larger files, run the formatter locally: node -e "console.log(JSON.stringify(JSON.parse(require('fs').readFileSync('input.json','utf8')),null,2))"

Yes — enable the 'Sort keys' option to sort object keys alphabetically at every level of nesting. Array element order is always preserved because arrays are ordered by definition.

Is my code or coverage data sent to a server?

No. The LCOV parser runs entirely in your browser in JavaScript. Your .info file is never uploaded — it is read and parsed locally. This makes the tool safe for proprietary codebases.

Which test runners and coverage tools produce LCOV output?

Jest (coverageReporters: ['lcov']), Vitest (coverage.reporter: ['lcov']), Istanbul/nyc (--reporter=lcov), gcov (with lcov CLI), coverage.py (coverage lcov), Cargo/tarpaulin (--out Lcov), and most CI coverage platforms including Codecov and Coveralls.

Tool comparison

JSON Formatter vs LCOV Coverage Viewer

JSON Formatter (formatting) and LCOV Coverage Viewer (validation) come from different categories but appear together in developer workflows. This guide explains what each does and when to reach for one over the other.

Bottom line

JSON Formatter is a general-purpose text transformation tool for any JSON document; LCOV Viewer renders code-coverage reports from lcov/genhtml output into a visual summary. Both are read-only display tools for different data formats: API debugging vs CI coverage analysis.

What each tool does

JSON Formatter

JSON (JavaScript Object Notation) is a lightweight text format for representing structured data using key-value pairs, arrays, strings, numbers, booleans, and null. It is the dominant data interchange format for REST APIs, configuration files, and data storage. A JSON formatter parses a JSON string and re-serializes it with consistent indentation and line breaks (pretty-print) to make it human-readable, or removes all whitespace (minify) to produce the smallest possible representation for transmission or storage. This tool goes further: it validates syntax and reports the exact line and column of any parse error, optionally sorts all object keys alphabetically for consistent diffs, and can repair common JSON-like inputs that are technically invalid — such as trailing commas, JavaScript-style comments, and single-quoted strings.

Open JSON Formatter →

LCOV Coverage Viewer

LCOV Coverage Viewer is a free online tool that parses LCOV .info files and displays a human-readable coverage report. LCOV is the standard output format for code coverage tools across many languages and test runners — including Jest (JavaScript), Istanbul/nyc (JavaScript), Vitest (TypeScript), gcov (C/C++), and coverage.py (Python). An LCOV .info file encodes line-by-line, function-by-function, and branch-by-branch execution data for every source file in your project. This tool reads that data and renders it as a sortable, filterable table showing which files are well-covered and which need more tests. Processing is entirely client-side — your source code and coverage data never leave your browser.

Open LCOV Coverage Viewer →

Side-by-side comparison

Feature	JSON Formatter	LCOV Coverage Viewer
Category	formatting	validation
Primary purpose	Pretty-print or minify JSON — with syntax validation.	Parse and visualize LCOV code coverage reports — line, function, and branch coverage per file.
Inputs	json, mode, indent, sort_keys, repair	lcov
Outputs	output, valid, error, error_line, error_column	summary, files

When to use each

Use JSON Formatter when…

How to pretty-print a JSON API response

Convert a minified or compact JSON API response into human-readable, indented output for inspection.

How to minify JSON for production

Remove all whitespace from a JSON file to reduce its size before embedding it in code, APIs, or config files.

Use LCOV Coverage Viewer when…

How to view a Jest LCOV coverage report online

Inspect Jest test coverage results from a lcov.info file without installing a local HTML viewer.

How to view an Istanbul/nyc coverage report online

Parse an LCOV .info file from Istanbul or nyc to visualize JavaScript coverage without serving HTML files.

Frequently asked questions

What's the file size limit?: The API endpoint accepts up to 1 MB of JSON per request. For larger files, run the formatter locally: node -e "console.log(JSON.stringify(JSON.parse(require('fs').readFileSync('input.json','utf8')),null,2))"
Does it sort keys?: Yes — enable the 'Sort keys' option to sort object keys alphabetically at every level of nesting. Array element order is always preserved because arrays are ordered by definition.
Is my code or coverage data sent to a server?: No. The LCOV parser runs entirely in your browser in JavaScript. Your .info file is never uploaded — it is read and parsed locally. This makes the tool safe for proprietary codebases.
Which test runners and coverage tools produce LCOV output?: Jest (coverageReporters: ['lcov']), Vitest (coverage.reporter: ['lcov']), Istanbul/nyc (--reporter=lcov), gcov (with lcov CLI), coverage.py (coverage lcov), Cargo/tarpaulin (--out Lcov), and most CI coverage platforms including Codecov and Coveralls.