Developer
Browse 22 professional tools
AI Playground
API Response Mocker
Chmod Calculator
Code Formatter & Beautifier
CORS Debugger
Docker Compose Builder
Git Command Builder
Git Commit Message Generator
Gitignore Generator
HTTP Status Codes Reference
JSON Schema Generator
JSON to TypeScript Converter
JSONPath Tester
JWT Builder
JWT Decoder
Regex Tester
SQL Formatter & Beautifier
SQL Playground
Test Credit Card Generator
User Agent Parser
XPath Tester
XSLT Transformer
The Developer category covers the tools you reach for during the actual programming day — formatting JSON, building regex patterns, decoding JWTs, debugging CORS, generating .gitignore files. The interesting question is not "do these exist elsewhere" (every dev tool has at least three online versions) but which ones you should reach for first, which are safe to paste production data into, and which are quietly wrong in ways that bite you later. These all run locally in the browser; nothing you paste leaves the page.
Parsing, validation, transformation
For testing expressions against real data. JSONPath and XPath have multiple dialects (RFC 9535 vs Jayway vs Goessner; XPath 1.0 vs 2.0/3.1) — verify against the exact engine your production code uses before shipping a query.
Test and debug regular expressions with real-time matching. Regex pattern builder with explanation. Free online regex tester for JavaScript, Python, PHP
Test JSONPath expressions with live results. Query JSON documents with JSONPath syntax. Free online JSONPath evaluator and debugger
Test XPath expressions on XML documents with live results. Debug XPath queries for web scraping. Free online XPath evaluator and validator
Generate JSON Schema from example JSON data automatically. Create validation schemas for APIs. Free online JSON Schema builder for developers
Generate TypeScript interfaces from JSON data. Support for nested objects, arrays, optional properties. Free online JSON to TS interface generator
Compare two JSON documents with visual tree diff. Highlight added, removed, modified nodes. Expandable tree view. Free online JSON comparison tool
Transform XML documents using XSLT stylesheets. Live preview of rendered HTML. Built-in templates for tables, cards, lists. Free online XSLT processor
Formatting
Beautifying minified JSON / SQL / code blobs. Prettier-compatible defaults; SQL dialect selection (Postgres / MySQL / SQLite / BigQuery) preserves dialect-specific quoting.
Format and beautify JSON, XML, CSS, HTML, JavaScript, SQL code. Auto-indent and syntax highlight. Free online code beautifier and formatter
Format and beautify SQL queries with syntax highlighting. Support for MySQL, PostgreSQL, SQL Server. Free online SQL formatter and pretty printer
Write and preview Markdown with live rendering. GitHub Flavored Markdown support. Free online Markdown editor with syntax highlighting
Create and edit Markdown tables visually. Import from CSV/Excel. Free online Markdown table maker with alignment options
Auth & API debugging
JWT pair lets you both inspect and construct test tokens. CORS debugger walks the same algorithm the browser uses (Fetch spec §3.2) so you can find the exact step where preflight or credentials handling breaks.
Decode and inspect JWT tokens. View header, payload, signature. Verify JWT expiration and claims. Free online JSON Web Token decoder and debugger
Generate JSON Web Tokens with custom claims. Support for HS256, HS384, HS512 algorithms. Set expiration, issuer, subject, audience. Free online JWT generator
Complete list of HTTP status codes with descriptions and examples. Learn 200, 301, 404, 500 error codes. Free HTTP response code reference guide
Debug CORS issues, analyze headers, generate server configurations. Support for Express, Nginx, Apache, Django, Flask, Spring Boot. Learn CORS concepts. Free online CORS tester
Generate mock API responses with fake JSON data. Create realistic REST API test data. Free mock server response generator for developers
Parse and analyze browser User-Agent strings. Detect browser, OS, device type from UA. Free online User-Agent decoder and analyzer
Git & deployment
Conventional Commits, common git recipes, and the few-second .gitignore generator that prevents node_modules ending up in history. Compose builder targets v2.x (the `version:` line is no longer needed).
Generate conventional commit messages following Angular, Conventional Commits standards. Create semantic git commits. Free commit message builder
Build Git commands interactively with options and flags. Learn branching, merging, rebasing with visualizations. Quick recipes for common Git workflows
Generate .gitignore files for any project. Templates for Node, Python, Java, Go, React, Vue, and more. Free online gitignore generator
Build docker-compose.yml files visually. Add MySQL, PostgreSQL, Redis, MongoDB services. Free online Docker Compose YAML generator
Systems & data
Unix permission math, CIDR subnet math, an in-browser SQLite playground via WebAssembly, and an LLM tokenization sandbox. The SQL playground handles 1-10M rows comfortably; beyond that switch to a real database.
Calculate Unix/Linux file permissions. Convert between symbolic (rwx) and numeric (755, 644) notation. Free chmod permission calculator online
Calculate IP subnets, network ranges, broadcast addresses, CIDR notation. IPv4 subnet mask calculator. Free online IP/CIDR calculator for network admins
Run SQL queries in your browser with SQLite. Import CSV files, create tables, export results. Free online SQL editor and database sandbox
Visual ERD designer for database schemas. Create tables, define relationships, foreign keys. Export to SQL for MySQL, PostgreSQL, SQLite. Free online ERD tool
Learn how AI language models work. Visualize tokenization, simulate temperature sampling, count tokens, build prompts. Interactive LLM tutorial and prompt engineering helper
Frequently asked questions
Why use a browser tool when I have the same thing locally?
Two reasons: zero-install for one-off uses, and pasting test data without it being in your shell history or in a temp file you forget to delete. For repeated daily work, native tools (jq, regex in your editor) are faster.
Are these safe to paste production data into?
Every tool in this category runs entirely in the browser tab — no upload, no logging, no telemetry on the inputs themselves. The page itself is served from the site; pasted text never reaches the server. The risk model is "is your browser trustworthy" which is the same risk model as any web app.
Which tools work offline?
All of them, once the page is loaded. The JS bundle runs entirely client-side; refreshing without internet still works as long as the browser cached the page. Useful when debugging from a hotel WiFi captive portal.
How do I pick between similar tools?
For format-conversion tasks (JSON ↔ TypeScript, sample → schema), pick the direction matching your workflow. For inspection tasks (JWT, regex, JSONPath), pick the one that matches the engine your production code uses — RFC 9535 JSONPath produces different results than Jayway JSONPath on the same input.
Last updated · E-Utils editorial team