Every developer has a collection of bookmarked tools. Regex testers, JSON formatters, base64 decoders, timestamp converters — the stuff you use three times a week but could never write from memory.
The problem is most online dev tools are terrible. They're covered in ads, they require accounts for basic functionality, they send your data to their servers, or they're so bloated they take ten seconds to load.
So here's a curated list of actually good free developer tools — organized by what you're trying to do, not alphabetically or by some arbitrary ranking. Every tool on this list is free, works without signup, and does its job without getting in the way.
Data Formatting & Conversion
JSON Formatter
You will use this tool more than any other. Paste minified JSON, get readable JSON. Simple.
The toolsto.dev JSON Formatter validates as you type and runs entirely in your browser. No data sent anywhere.
Also useful for: Validating API responses, debugging malformed JSON, cleaning up config files.
SQL Formatter
Raw SQL from an ORM is unreadable. Paste it, get it formatted with proper indentation and keyword capitalization.
toolsto.dev SQL Formatter supports MySQL, PostgreSQL, SQL Server, and other dialects.
CSV to JSON
Because the data always comes as CSV and the API always wants JSON.
toolsto.dev CSV to JSON handles headers, custom delimiters, and nested structures.
JSON to TypeScript
Paste a JSON response, get TypeScript interfaces. Saves 20 minutes of manually typing out types for every new API integration.
toolsto.dev JSON to TypeScript generates clean, nested interfaces with optional properties.
Encoding & Decoding
Base64 Encoder/Decoder
Base64 shows up everywhere — JWTs, data URIs, email attachments, API payloads. You'll decode it at least once a week.
toolsto.dev Base64 Encoder handles both encode and decode, with support for UTF-8 text and file uploads.
URL Encoder/Decoder
Query strings with special characters break unless they're properly encoded. This tool encodes and decodes URL components.
toolsto.dev URL Encoder — paste a URL or query string, get the encoded/decoded version.
JWT Decoder
JWTs are base64-encoded JSON with a signature. You can't just base64-decode them because of the URL-safe encoding. A JWT decoder splits the header, payload, and signature and shows you what's inside.
toolsto.dev JWT Decoder decodes the token client-side and displays expiration time, claims, and algorithm.
Text & String Tools
Regex Tester
Regular expressions are the tool you use when no other tool works. A regex tester lets you write a pattern, test it against sample text, and see matches highlighted in real-time.
toolsto.dev Regex Tester supports JavaScript regex with flags, capture groups, and match highlighting.
Word & Character Counter
For commit messages (72 chars), tweets (280 chars), meta descriptions (155 chars), and any other time you need to know exactly how long a string is.
toolsto.dev Word Counter shows words, characters, sentences, and paragraphs — live as you type.
Text Diff Checker
Comparing two versions of a file, config, or API response. Paste both, see what changed.
toolsto.dev Text Diff shows additions, deletions, and modifications with syntax highlighting.
Case Converter
Convert between camelCase, snake_case, UPPER_CASE, Title Case, and more. Useful when you're porting code between languages with different naming conventions.
toolsto.dev Case Converter handles all common case formats with one click.
Find & Replace
Like your editor's find-and-replace, but for quick text transformations without opening a file. Supports regex.
toolsto.dev Find & Replace — paste text, find pattern, replace, copy result.
Crypto & Security
Hash Generator
Generate MD5, SHA-1, SHA-256, and SHA-512 hashes from text or files. Used for verifying file integrity, comparing passwords, and debugging webhook signatures.
toolsto.dev Hash Generator generates all common hash algorithms simultaneously.
HMAC Generator
HMAC is a keyed hash — used for API authentication, webhook verification, and message signing. Most payment APIs (Stripe, PayPal) use HMAC signatures.
toolsto.dev HMAC Generator supports all SHA variants with a secret key input.
Password Generator
Generates cryptographically random passwords with configurable length, character types, and exclusions.
toolsto.dev Password Generator runs entirely in your browser using the Web Crypto API — no passwords ever leave your device.
Generators
UUID Generator
Need a unique ID? UUIDs (v4) are 128-bit random identifiers with a vanishingly small collision probability.
toolsto.dev UUID Generator generates v4 UUIDs in bulk with one click.
Lorem Ipsum Generator
Placeholder text for mockups, designs, and testing layouts.
toolsto.dev Lorem Ipsum Generator generates paragraphs, sentences, or words.
Dev Reference
HTTP Status Codes
Every developer needs to look up HTTP status codes constantly. What's the difference between 401 and 403? When do you use 204 vs 200? What does 502 actually mean?
toolsto.dev HTTP Status Codes — searchable reference with descriptions and use cases for every code.
Cron Expression Explainer
Cron syntax is cryptic. 0 */6 * * 1-5 — is that every 6 hours on weekdays? Every 6 minutes? Paste a cron expression, get a human-readable explanation.
toolsto.dev Cron Explainer translates cron expressions into plain English with next run times.
Chmod Calculator
Unix file permissions in octal notation. Convert between symbolic (rwxr-xr-x) and numeric (755) formats.
toolsto.dev Chmod Calculator — click checkboxes, get the octal value. Or type a number, see the permissions.
Color Converter
Convert between HEX, RGB, HSL, and other color formats. Preview the color visually.
toolsto.dev Color Converter handles all common web color formats with a visual preview.
What's My IP
Quick check of your public IP address, ISP, and approximate location. Useful for debugging network issues, VPN verification, and firewall configuration.
toolsto.dev What's My IP — instant IP lookup with no tracking.
Why Client-Side Matters
Most of the tools listed above run entirely in your browser. That means:
- Your data never leaves your device. No server receives your JSON, your JWT tokens, your passwords, or your hashes.
- They work offline. Once loaded, they don't need a network connection.
- They're fast. No round-trip to a server. Processing happens instantly on your machine.
This matters more than people realize. Developers routinely paste production API keys, JWT tokens with user data, database connection strings, and other sensitive information into online tools. If that tool sends your input to a server, you've just shared that data with a third party.
All 26 tools on toolsto.dev run client-side. Your data stays on your device. That's the whole point.