Formalint

Browser-based developer tools

JSON Diff Viewer

Compare two API responses, configs or payloads side by side without sending input to a backend.

Open JSON formatter

Left JSON

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Right JSON

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Diff

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JSON FormatterFormat, validate and inspect JSON JSON SchemaGenerate schema drafts Regex TesterPattern matching and groups JWT DecoderInspect token claims

Reference notes

Compare API responses without context switching

Field-level changes

The diff highlights added, removed and changed values by JSON path so you can spot response changes quickly.

Local-first review

Both snippets are parsed in the browser. Formalint does not upload pasted JSON to a backend for comparison.

API debugging

Use it when comparing staging and production responses, webhook retries, config versions or before-and-after payloads.