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jsonfmt.dev
What it is
jsonfmt.dev is an online JSON formatter, beautifier, and validator with browser tools and an HTTPS API. Formatting options include 2-space or 4-space indentation, tabs, key sorting, and depth control. The site says its validator checks JSON against RFC 8259 and reports line and column errors. Additional tools repair common malformed JSON, compare documents, and convert formats such as YAML, CSV, XML, TypeScript, SQL, GraphQL, and Protobuf. The toolkit also includes a JWT decoder, JSON Schema validator, JSONPath evaluator, and JSONL tools. The maker says the core web tool handles JSON locally in the browser, works offline after loading, and can be installed as a Progressive Web App. Its API supports formatting, minifying, validation, repair, diffing, conversion, and other endpoints. Anonymous API use is limited to 10 requests per minute; a free API key allows 100 requests per minute and 1,000 requests per month. Pro API access costs $9, paid once and allows 1,000 requests per minute and 50,000 requests per month. Share links put JSON in the URL fragment, accessible to anyone with the link.
For and against
For
- Formatting supports indentation choices, key sorting, and depth control.
- Validator reports line and column errors.
- Includes repair, comparison, and format conversion tools.
- Core web tool processes JSON locally, according to the maker.
- Offline use is available after loading.
Against
- Anonymous API use is limited to 10 requests per minute.
- Free API key is limited to 1,000 requests per month.
- Anyone with a share link can access its contents.
- Site uses Google Analytics and Google AdSense, which may use cookies.
The verdict
The browser toolkit combines JSON formatting and validation with repair, comparison, conversion, and related tools. API users should compare the request limits, and anyone sharing a link should consider that its contents are accessible to link holders.
Who it suits
jsonfmt.dev suits people who want browser-based tools for formatting, checking, repairing, comparing, or converting JSON. Its API options also suit developers who need programmatic access, with limits that differ by tier.
Plans and prices
Anonymous API
10 requests/minute · all endpoints · no monthly limit · community support
Read 2 Oct 2026 · api.jsonfmt.dev
Free API key
100 requests/minute · all endpoints · 1,000 requests/month · email support
Read 2 Oct 2026 · api.jsonfmt.dev
Pro API
1,000 requests/minute · all endpoints · 50,000 requests/month · priority support
Read 2 Oct 2026 · api.jsonfmt.dev
On the record
- Analytics and ads
- The privacy policy says the site uses Google Analytics and Google AdSense, which may use cookies; it also says local tool preferences and session data are kept in browser localStorage.jsonfmt.dev · read 2 Oct 2026
- API access
- The API accepts JSON over HTTPS and offers formatting, minifying, validation, repair, diffing, conversion, and other endpoints.api.jsonfmt.dev · read 2 Oct 2026
- API limit
- Unauthenticated API use is limited to 10 requests per minute; the documentation lists a free API-key tier at 100 requests per minute and 1,000 requests per month.api.jsonfmt.dev · read 2 Oct 2026
- Conversion
- The site lists converters for formats including YAML, CSV, XML, TypeScript, SQL, GraphQL, and Protobuf.jsonfmt.dev · read 2 Oct 2026
- Formatting
- The formatter supports 2-space, 4-space, or tab indentation, optional key sorting, and depth control.jsonfmt.dev · read 2 Oct 2026
- Integrations
- The maker describes an MCP server package, jsonfmt-mcp, that exposes JSON-processing tools to MCP-compatible AI clients.jsonfmt.dev · read 2 Oct 2026
- Offline use
- The site says it works offline after loading and can be installed as a Progressive Web App.jsonfmt.dev · read 2 Oct 2026
- Other tools
- The web toolkit also includes a JWT decoder, JSON Schema validator, JSONPath evaluator, and JSONL tools.jsonfmt.dev · read 2 Oct 2026
- Privacy
- The maker says the core web tool processes JSON locally in the browser and does not send JSON content to its servers.jsonfmt.dev · read 2 Oct 2026
- Product
- jsonfmt.dev describes itself as a free online JSON formatter, beautifier, and validator.jsonfmt.dev · read 2 Oct 2026
- Repair and diff
- Its tools can repair common malformed JSON and compare two documents, highlighting added, removed, and changed fields.jsonfmt.dev · read 2 Oct 2026
- Share links
- Share links encode JSON in the URL fragment, which the policy says is not sent in HTTP requests; anyone with the link can access its contents.jsonfmt.dev · read 2 Oct 2026
- Support
- The API pricing lists community support for anonymous access, email support for the free key tier, and priority support for Pro.api.jsonfmt.dev · read 2 Oct 2026
- Validation
- The site says it validates JSON against RFC 8259 and reports precise line and column errors.jsonfmt.dev · read 2 Oct 2026
