Essential tools for developers. Format, encode, decode, generate, and test directly in your browser. No installation required.
Every developer hits the same speed bumps: a JSON payload that won't parse, a token that needs inspecting, a config file in the wrong format, a hash that needs verifying. This collection of free developer tools exists to clear those bumps in seconds — format, encode, decode, generate, and compare, all directly in your browser with no installation, no account, and no data leaving your machine. Each tool is a single-purpose page that does one job well, the way command-line utilities do, but available the moment you need them regardless of what language or stack you work in.
The collection is organized into four working groups. Diagrams render Mermaid syntax live — flowcharts, sequence, class, and ER diagrams with SVG export. Encoding & format tools move data between representations: JSON, Base64, URLs, JWTs, YAML, and HTML forms. Generators create the artifacts developers reach for daily: hashes, UUIDs, QR codes, placeholder images, and SEO meta tags. Text & data tools handle the comparison and conversion work that fills the gaps — diffs, word counts, SQL formatting, and number conversions. Together they cover the small, repetitive tasks that otherwise fragment your focus across a dozen tabs.
The quickest way to pick the right tool is to look at what you have in hand and what you need out. The table below maps every tool in this directory to its core inputs and outputs, exactly as each tool page describes them.
| Tool | Key input | Output |
|---|---|---|
| JSON Formatter | Raw or minified JSON string | Formatted, validated, indented JSON |
| Base64 Encoder | Any text | Base64-encoded text, and decoded back |
| URL Encoder | URL or query-string text | Percent-encoded URL-safe text |
| JWT Decoder | A JSON Web Token | Decoded header and payload claims (no signature verification) |
| YAML to JSON | YAML document | Equivalent JSON |
| Form Builder | Field definitions | Generated HTML form markup |
| Hash Generator | Any text | MD5, SHA1, and SHA256 digests |
| UUID Generator | Count of IDs needed | Random UUID (v4) values |
| QR Code Generator | Text or URL | Scannable QR code image |
| Placeholder Images | Dimensions and options | Development placeholder images |
| Meta Tag Generator | Title, description, URL | SEO meta tag HTML |
| Text Diff | Two blocks of text | Line-by-line differences |
| Number to Words | A number | The number spelled out in words |
| Roman Numerals | Number or numeral | Converted value in the other notation |
| SQL Formatter | SQL query text | Formatted, consistently indented SQL |
| Word Counter | Any text | Word and character counts |
The encoding group is the workhorse of the collection. The JSON Formatter is the tool most developers reach for first: paste a response body or config snippet and it validates the syntax and reformats it with clean indentation, so a missing comma or unbalanced bracket becomes obvious instead of hiding in a wall of minified text. Because validation and formatting happen together, it doubles as a syntax checker before you commit a hand-edited JSON file.
The Base64 Encoder handles the encoding scheme that shows up everywhere in web work — data URIs, HTTP basic authentication headers, and embedded binary payloads. It works in both directions, encoding text to Base64 and decoding it back. The URL Encoder solves the parallel problem for URLs: converting spaces, ampersands, and unicode into percent-encoded sequences that survive a trip through a query string, and back again.
The JWT Decoder is built for API debugging. A JSON Web Token is three Base64url segments — header, payload, signature — and the decoder unpacks the first two into readable JSON so you can check the exp claim on an expiring token, confirm the issuer, or see which scopes were granted. It is an inspection tool: it does not verify signatures, which requires the signing key held by your authorization server. The YAML to JSON converter rounds out the group, translating YAML — the format of choice for Kubernetes manifests, CI pipelines, and much modern config — into the JSON that APIs, policy engines, and validators expect.
The generator group produces the artifacts you would otherwise write utilities for. The Hash Generator computes MD5, SHA1, and SHA256 digests from any text, entirely in your browser — useful for checksum comparisons, cache keys, and verifying that two strings really are identical. The UUID Generator produces random version-4 UUIDs, the standard unique identifier for database records, distributed systems, and API keys when you need one (or a batch) right now.
The remaining generators cover visual and markup output. The QR Code Generator turns any text or URL into a scannable code; the Placeholder Image Generator produces the grey-box stand-in images that fill layouts during development; and the Meta Tag Generator assembles SEO-ready title, description, and Open Graph tags from the fields you supply, saving you from hand-writing the same boilerplate for every page.
The text and data group handles the comparison and cleanup jobs that punctuate a coding day. Text Diff compares two blocks of text line by line and highlights what changed — invaluable when a config worked yesterday and doesn't today, or when reviewing a patch outside a git client. The SQL Formatter takes a gnarly one-line query and restores the indentation that makes joins and subqueries readable. The Word Counter gives instant word and character counts — the same tool appears in our everyday collection because writers need it too — and Number to Words and the Roman Numeral Converter handle the two notation conversions that come up in invoicing, legal text, outlines, and copyright lines.
Finally, the Form Builder generates HTML form markup from field definitions without drag-and-drop complexity — describe the fields you need and copy out the markup.
If you have malformed or minified JSON, start with the JSON Formatter. If you are debugging authentication, use the JWT Decoder to read claims and the Base64 Encoder to decode other encoded values. For config conversion, YAML to JSON. For integrity checks, the Hash Generator's MD5/SHA1/SHA256 output. For change hunting, Text Diff. And when you need generated identifiers or markup — UUIDs, QR codes, placeholder images, meta tags, or form HTML — the generators deliver without a single dependency added to your project. Bookmark the ones you use weekly; the rest will be here when the need shows up.