webtoolz
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JSON Studio & Mock API Builder — the complete developer toolkit

webtoolz gives you two flagship tools: JSON Studio for formatting, validating, comparing, converting, and repairing JSON, and Mock API Builder for creating multi-endpoint REST APIs — all without uploading data to a server. Every tool runs 100% in your browser using JavaScript, so your data stays on your device. No sign-up, no rate limits, no tracking.

JSON Studio

Format, minify, validate, and explore JSON with syntax highlighting and tree view

Schema Validator

Validate JSON documents against JSON Schema draft 2020-12 and earlier

JSON to CSV

Export JSON arrays to CSV with configurable delimiters and nested object flattening

JSON to YAML

Convert JSON to YAML for Kubernetes manifests and configuration files

YAML to JSON

Parse YAML files and output formatted JSON for APIs and data processing

JSON Diff

Find structural differences between two JSON documents with highlighted changes

Mock API Builder

Build multi-endpoint mock REST APIs with path params, conditional responses, dynamic templates, and Faker.js data

Why webtoolz?

  • Privacy-first — all processing happens client-side, nothing is sent to a server
  • No sign-up or account required — open the page and start working
  • Works offline after the first load — no internet dependency for core tools
  • AI-powered JSON repair fixes broken syntax from copy-paste, trailing commas, and unquoted keys
  • Mock API Builder — create multi-endpoint REST APIs with path params, conditional responses, and Faker.js data for frontend prototyping

Frequently asked questions

Are webtoolz JSON tools free?
Yes, completely free with no usage limits. There are no premium tiers, no rate limiting, and no ads. The tools are open to everyone — developers, students, and teams alike.
Is my data safe?
Your data never leaves your browser. All formatting, validation, diffing, and conversion runs client-side in JavaScript. Nothing is sent to a server, stored, or logged. This makes webtoolz safe for sensitive data, API keys, and internal configuration files.
Do the tools work offline?
Core tools (formatter, validator, diff, converters) work offline after the initial page load. AI-powered features like JSON repair require a network connection since they use a language model, but all other operations are purely client-side.
What JSON standards are supported?
The tools support standard JSON (RFC 8259), JSON5 for lenient parsing, JSON Schema draft 2020-12 / draft-07 / draft-06 / draft-04 for validation, and YAML 1.2 for conversion. CSV output follows RFC 4180.
What is the Mock API Builder?
The Mock API Builder lets you create multi-endpoint REST APIs directly in your browser. Define GET, POST, PUT, and DELETE endpoints with path parameters, conditional responses, dynamic templates, and Faker.js-generated data. Share your entire API via a single URL — no server, no deployment, no expiry.