Free Online Developer Tools
Free developer tools for formatting JSON, testing APIs, generating UUIDs, converting data formats, debugging code, and improving development workflows. All tools run directly in your browser with no sign-up or installation required.
Updated June 3, 2026
JSON Formatter
Format & validateFormat, validate, minify, and syntax-highlight JSON. Live parsing with sort keys and download support.
Diff Checker
Compare text & codeCompare two texts side-by-side with LCS-based diffing. Split, unified, and char-level inline modes.
Regex Tester
Test & debug patternsLive regex match highlighting, capture group table, replace mode with $1/$<name> references, 10 presets, and a quick-reference panel. All JS flags supported.
Base64 Encoder/Decoder
Encode & decode instantlyEncode text or files to Base64 and decode Base64 strings back to text or images. Standard, URL-safe, and MIME variants. 100% client-side.
UUID / ULID / NanoID
v4, v7, v1, ULID, NanoIDGenerate UUID v4, v7, v1, ULID, and NanoID in bulk. Uppercase, no-hyphens, custom NanoID alphabet. Up to 1000 IDs, copy all or download. 100% browser, no sign-up.
Password Generator
Secure & entropy-scoredGenerate cryptographically secure passwords, passphrases, PINs, and memorable passwords. Live entropy meter, crack-time estimate, bulk generation, and copy history.
Hash Generator
MD5 · SHA-256 · SHA-512Generate MD5, SHA-1, SHA-256, SHA-384, and SHA-512 hashes from text or files. HMAC mode, hash verification, uppercase toggle, copy-all. 100% client-side.
JWT Decoder
Decode & verify tokensDecode JWT header and payload, read all claims with descriptions, verify HS256 signatures, and check expiry with a live countdown. 100% client-side.
URL Encoder/Decoder
Percent-encode & decodeEncode and decode URLs and query strings. Supports encodeURIComponent (query params) and encodeURI (full URLs). Highlights %XX sequences live.
Timestamp Converter
Epoch → date, batch, timezonesConvert Unix timestamps to ISO 8601, UTC, RFC 2822, relative time and more. Supports seconds, milliseconds, microseconds. Timezone picker, batch converter, live clock.
Cron Expression Builder
Visual cron generator & schedulerBuild and validate cron expressions visually. Point-and-click field builder, instant human-readable descriptions, next 6 run times, 16 presets, and full POSIX syntax support.
API Request Generator & Tester
Generate · Test · 12 langsGenerate HTTP request code in 12 languages and test APIs live in the browser — Fetch, Axios, XHR, Node.js, cURL, Python, PHP, Ruby, Go, C#, Jest, Pytest. GraphQL, env vars, history & Postman import.
Database Schema Designer
Templates · Indexes · SQL dialectsDesign database tables, fields, indexes, keys, and relationships visually. Start from SaaS, ecommerce, or CRM templates and export PostgreSQL, MySQL, SQLite, Prisma, Mongoose, and Firestore code.
YAML ↔ JSON Converter
Bidirectional, auto-detectConvert YAML to JSON or JSON to YAML instantly. Auto-detects input format, syntax-highlighted output, sort keys, copy & download. Full YAML 1.2 support.
CSV → JSON Converter
Table preview & type inferenceConvert CSV to JSON or JSON to CSV instantly. Auto-detects format, infers types, live table preview, multiple delimiters, copy & download. RFC 4180 compliant.
HTML Formatter
Prettify HTML, CSS & JSPaste HTML and format it instantly with proper indentation. Prettifies inline <style> CSS and <script> JS. Line numbers + history.
JavaScript Minifier
Concatenate, uglify & compressMinify JavaScript online in your browser. Concatenate multiple JS files, remove comments, compress whitespace, optionally uglify variable names, wrap in an IIFE, and download a .min.js file.
SQL Formatter
Beautify & minify SQLFormat and beautify SQL queries with proper indentation, keyword casing, and syntax highlighting. Minify SQL, dialect support for MySQL, PostgreSQL, SQLite & SQL Server.
Tailwind Formatter
Sort & group classesSort, deduplicate, and group Tailwind CSS classes by category. Flat and grouped output views.
JSON → TypeScript
Interface & type generatorPaste JSON and get TypeScript interfaces or type aliases instantly. Handles nested objects, arrays of objects, optional fields, null safety, export keyword, and custom root names.
HTML → JSX Converter
Convert HTML to ReactConvert HTML to React JSX. Handles className, htmlFor, camelCase events, self-closing tags, and inline styles.
JSON Table Viewer
Tabular JSON explorerVisualize JSON arrays as tables. Filter, sort, paginate, toggle columns, and export as CSV.
JSON Dashboard Generator
Charts · filters · React exportPaste any JSON or API response — instant stat cards, bar/line/pie charts, category filters, sortable table, and a complete React dashboard with Recharts. No setup required.
Code Screenshot
Beautiful code imagesTurn any code snippet into a stunning PNG. 9 themes, 22 languages, macOS/Windows/Terminal frames, gradient backgrounds. Download at 1×/2×/3× scale.
Meta Tag Generator
SEO · OG · Twitter · JSON-LDGenerate complete meta tag sets from page details. Live Google SERP, Facebook OG, and Twitter card previews. Export as HTML, Next.js metadata, React Helmet, Vue/Nuxt, Astro, or JSON-LD.
Robots.txt Generator
Crawl rules + sitemapGenerate a clean robots.txt file with Allow, Disallow, Crawl-delay, Host, and Sitemap directives. Includes public site, staging, and ecommerce presets with copy and download output.
Sitemap.xml Generator
XML sitemap creatorCreate a valid sitemap.xml file from URLs or paths. Add lastmod, changefreq, and priority fields, then copy or download the XML for search engines.
.htaccess Redirect Generator
301, 302, HTTPS, wwwGenerate Apache .htaccess redirect rules for custom 301 and 302 redirects, HTTPS enforcement, www/non-www canonical hosts, and trailing slash handling.
Schema Markup Generator
JSON-LD structured dataGenerate JSON-LD schema markup for WebSite, Article, Product, FAQPage, and LocalBusiness pages with ready-to-paste script output.
Hreflang Tag Generator
International SEO tagsGenerate hreflang alternate tags for multilingual and regional pages. Output HTML link tags or sitemap XML alternates with x-default support.
Security Headers Generator
CSP, HSTS, permissionsGenerate security header configuration for Apache, Nginx, and Next.js, including CSP, HSTS, X-Frame-Options, Referrer-Policy, and Permissions-Policy.
LLMs.txt Generator
AI discovery fileCreate an llms.txt draft for AI crawlers and assistants with site description, important canonical pages, sitemap link, and usage notes.
API Mock Generator
Fake REST API with JSON schemaBuild fake REST API endpoints with realistic mock JSON. Auto-generate fake data, export as JSON Server db.json or Postman collection. Free for frontend devs.
Responsive Preview
Test any screen sizePreview any website at 8 screen sizes from 320px mobile to 1920px wide. Zoom controls and device tabs.
Markdown Editor
Live preview & GFM exportWrite Markdown with a real-time GitHub Flavored Markdown preview. Toolbar shortcuts, localStorage auto-save, export as .md or standalone .html. 100% browser, no sign-up.
About this tool
About Developer Tools
These developer tools cover the everyday workflows of front-end and full-stack developers — formatting, validation, conversion, testing, and encoding — all running entirely in the browser. No installation, no server, no API key required.
Data Formatting and Conversion
The JSON Formatter validates, formats, minifies, and sorts JSON from any source. Paste from an API response or config file and get clean, indented output instantly. The JSON Table Viewer visualises JSON arrays as searchable, sortable tables — useful for scanning large datasets without a spreadsheet. JSON to TypeScript generates strongly-typed interfaces from any JSON object, handling nested objects, optional fields, and arrays. JSON Dashboard Generator converts a JSON payload or live API URL into instant charts and stat cards.
SQL Formatter beautifies MySQL, PostgreSQL, SQLite, T-SQL, and BigQuery queries. YAML ↔ JSON and CSV ↔ JSON converters translate between common data formats with one paste and one click.
The JavaScript Minifier adds a quick browser-based workflow for compressing scripts, concatenating multiple uploaded JS files, preserving license comments, optionally uglifying simple identifiers, and downloading a .min.js file without sending source code to a server.
Security, Encoding, and Identity
The Hash Generator computes MD5, SHA-1, SHA-256, and SHA-512 digests using the browser's built-in SubtleCrypto API — no data sent anywhere. The Base64 Encoder / Decoder handles text, files, and Data URIs. The JWT Decoder splits any JSON Web Token into its parts, displays all claims with human-readable labels (including a live expiry countdown), and verifies HS256 signatures. The Password Generator creates cryptographically random passwords with entropy scoring. The UUID / ULID / NanoID Generator produces v4, v7, and v1 UUIDs, ULIDs, and NanoIDs in bulk — up to 1,000 at once.
API Development and Testing
The API Request Generator & Tester builds HTTP requests with custom headers, body, authentication, and query parameters, executes them live in the browser, and generates equivalent code in 12 languages — cURL, Fetch, Axios, Python requests, Go, PHP, Ruby, and more. The API Mock Generator creates fake REST API responses from a JSON schema — export as a JSON Server db.json for a local mock API or as a Postman collection.
Developer Utilities
The Diff Checker compares two text blocks using LCS diffing in split, unified, or character-level inline views. The Regex Tester provides live match highlighting with group extraction and a flags panel. The Cron Expression Builder translates between human-readable schedules and cron syntax, showing the next 5 run times. The Timestamp Converter handles Unix timestamps, ISO 8601, and human-readable dates across time zones. The Meta Tag Generator outputs a complete HTML head block with Open Graph, Twitter Card, and core meta tags.
Private by Design
Every tool in this collection runs client-side with no data uploaded to any server. Your JSON, code, API responses, JWT tokens, and passwords never leave your browser. This makes them safe for use with sensitive configuration files, internal API responses, authentication tokens, and production data during debugging — situations where sending data to a third-party cloud service is not acceptable. There are no accounts, no rate limits, and no paid tiers. Open the tool, paste your data, and get results instantly.
Real-world uses
Common Use Cases
Got questions?
Frequently Asked Questions
No. Every tool in this collection processes data entirely in your browser using standard JavaScript APIs. JSON, code snippets, passwords, JWT tokens, and API payloads never leave your device. Security-sensitive tools like Hash Generator and Password Generator use the browser's built-in SubtleCrypto API, which runs natively with no network requests.
Yes. The API Request Generator & Tester lets you build requests with custom headers, body (JSON, form-data, raw), authentication (Bearer, Basic, API Key), and query parameters, then execute them live in the browser using the Fetch API. Inspect the full response including status code, headers, and JSON body. It also generates equivalent code in 12 programming languages.
The JWT Decoder splits any JWT into its three base64url-encoded parts, decodes the header and payload, and displays all claims with human-readable labels — including exp (expiry with a live countdown timer), iat (issued at), nbf, sub, aud, iss, and all custom claims. It also verifies HS256 signatures if you provide the signing secret.
The UUID / ULID / NanoID Generator supports UUID v4 (cryptographically random), UUID v7 (time-ordered, sortable), UUID v1 (time-based with MAC address), ULID (Universally Unique Lexicographically Sortable Identifiers), and NanoID with a configurable alphabet. Generate up to 1,000 IDs at once with uppercase, no-hyphens, and copy-all options.
Paste two text blocks into the left and right panels. The tool uses LCS (Longest Common Subsequence) diffing to identify added, removed, and unchanged lines. Switch between split view (side by side), unified view (GitHub-style +/- lines), and character-level inline highlighting to see exactly what changed between two versions.
Yes. The API Mock Generator lets you define a JSON schema with field types like name, email, date, UUID, number range, boolean, and image URL. It generates a realistic fake dataset of any size. Export as a JSON Server db.json (run npx json-server db.json for a local REST API) or as a Postman collection.
The JSON to TypeScript converter analyses nested objects, arrays, and mixed-type fields. It generates named interfaces for each nested object, marks fields as optional when they are null or missing in the sample, and handles arrays of primitives and arrays of objects correctly. The output is valid TypeScript ready to paste into a .ts or .d.ts file.
The Cron Expression Builder translates cron syntax (e.g. 0 9 * * 1-5) into plain English and back. Use it to write scheduled job expressions for GitHub Actions, AWS EventBridge, Kubernetes CronJobs, or any Unix cron daemon without memorising the field order. It shows the next 5 scheduled run times so you can verify the expression before deploying.