10 free browser-based developer tools that run locally with no signup. JSON formatter, regex tester, JWT decoder, diff checker, and more — all in one place.
The best developer tools run in your browser, require no signup, and never send your data to a server. After building 90+ free tools at WOWHOW, we’ve identified the 10 that developers use most frequently. Each solves a daily pain point: formatting messy JSON, testing regex patterns, decoding JWTs, comparing code diffs, and more. All of them run entirely client-side — your data never leaves your browser.
1. JSON Formatter & Validator
Every developer works with JSON daily. Our free JSON formatter takes messy, minified, or invalid JSON and formats it with proper indentation, syntax highlighting, and validation. It catches missing commas, mismatched brackets, and type errors instantly.
Why developers use it: API responses, config files, and database outputs are often single-line JSON blobs. Pasting into a formatter with syntax highlighting makes the structure immediately visible. The validator catches errors that your IDE might miss, especially in deeply nested objects.
2. Regex Playground
Regular expressions are powerful but notoriously hard to get right. The regex playground lets you test patterns against sample text in real-time, with match highlighting, capture group visualization, and a cheatsheet of common patterns.
Why developers use it: Writing regex blind and testing in production is a recipe for bugs. A visual playground where you can see matches update as you type catches edge cases before they reach your codebase. The built-in cheatsheet saves trips to Stack Overflow for syntax you use once a month.
3. JWT Decoder
JSON Web Tokens are everywhere in modern auth systems, but they’re base64-encoded and unreadable without a decoder. Our JWT decoder parses the header, payload, and signature, showing expiration times, claims, and issuer information in a readable format.
Why developers use it: When debugging auth issues, you need to see what’s inside the token. Is it expired? Does it have the right scope? Is the issuer correct? A one-click decode answers these questions in seconds instead of writing custom parsing code.
4. Diff Checker
Comparing two versions of code, config, or text is a constant need. The diff checker provides side-by-side and inline diff views with syntax highlighting, showing additions, deletions, and modifications clearly.
Why developers use it: Git diff is great for committed changes, but comparing arbitrary text — two API responses, two config files, a before/after of a database query result — requires a standalone diff tool. Browser-based means no installation and no file management.
5. Base64 Encoder/Decoder
Base64 encoding appears in APIs, email attachments, data URIs, and authentication headers. The Base64 encoder/decoder handles text-to-base64 and base64-to-text conversions instantly, with support for URL-safe encoding.
Why developers use it: Debugging API integrations where payloads are base64-encoded requires fast decode/encode cycles. This is especially common when working with webhooks, OAuth tokens, and email APIs.
6. UUID Generator
UUIDs are the standard for unique identifiers in distributed systems. The UUID generator creates v4 UUIDs in bulk, with copy-to-clipboard and format options.
Why developers use it: Database seeding, API testing, and mock data generation all require unique IDs. Generating them in-browser is faster than writing a script or importing a library for a one-off need.
7. Hash Generator
The hash generator computes MD5, SHA-1, SHA-256, and SHA-512 hashes of any text input. Useful for verifying file integrity, generating test checksums, and understanding hash-based security.
Why developers use it: Verifying that a downloaded file matches its published checksum, generating test password hashes, or computing content hashes for cache keys — all common tasks that require a quick hash without installing command-line tools.
8. cURL to Code Converter
The cURL to code converter transforms cURL commands into working code in Python, JavaScript, Go, PHP, and more. Paste a cURL command from browser DevTools or API docs and get production-ready code.
Why developers use it: API documentation often provides cURL examples, but you need the equivalent in your language. Manual translation is error-prone, especially with complex headers, authentication, and request bodies. Automated conversion eliminates typos and missed parameters.
9. Password Generator
The password generator creates cryptographically strong passwords with configurable length, character sets, and memorable passphrase options.
Why developers use it: Service accounts, API keys, database passwords, and test credentials all need strong, unique passwords. Generating them in-browser with no server involvement means the passwords never leave your machine.
10. Markdown Editor
The markdown editor provides a split-pane view with live preview, syntax highlighting, and export to HTML. Perfect for README files, documentation, and blog posts.
Why developers use it: Writing markdown without preview leads to formatting mistakes. A live preview editor catches issues before you commit, and the HTML export is useful for pasting into CMS systems that don’t support markdown natively.
Why Browser-Based Tools Matter
Three reasons browser-based developer tools are superior to installed alternatives:
- Security: Your data never leaves your device. When decoding JWTs, formatting API responses, or generating passwords, the computation happens entirely in JavaScript on your machine. No server sees your sensitive data.
- Availability: No installation means they work on any machine — your work laptop, a client’s machine, a shared server. Bookmark the URL and the tool is always available.
- Speed: No app startup time, no updates to install, no accounts to manage. Open the URL, use the tool, close the tab.
All 90+ WOWHOW tools follow these principles. Browse the full collection at /tools — every tool is free, requires no signup, and runs entirely in your browser.
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