Browser bookmarks, package managers, and cloud dashboards get most of the attention. But the tools that actually eat hours in a developer's day are the small, specific ones: the JSON formatter you open when an API response is 600 characters of minified text, the timestamp converter that saves you from epoch arithmetic, the Base64 decoder that shows you what's inside that Authorization header.
at-use.com has 29 browser-based developer tools live today. No login required, nothing stored beyond what the conversion needs, and the ones that genuinely need server-side processing (YAML parsing, CSS validation) run server-side without logging your input.
This is the complete list.
JSON, YAML & XML
JSON Formatter & Validator
Format or minify JSON using the browser's own JSON.parse(). Syntax errors return the exact line and column. Three modes: format (2-space indent), minify (one line), validate. Nothing leaves your browser tab.
Tip: Minify mode collapses formatted JSON back to a single line — useful before pasting it into a curl command or a config value.
JSON Diff Checker
Compare two JSON objects and see exactly what changed: added keys in green, removed in red, changed values in yellow. Deep recursive diff at every nesting level. Side-by-side and unified views. "Ignore key order" option treats {"a":1,"b":2} and {"b":2,"a":1} as identical.
Tip: Run both objects through the JSON Formatter first. Normalised indentation means the diff shows real differences, not whitespace noise.
JSON to YAML Converter
Converts any JSON object to YAML in the browser using js-yaml (MIT). Useful for moving API responses into Kubernetes or Helm config files without installing a library.
Tip: Deep nested objects convert cleanly — check the output indent depth if the target YAML file expects 4-space indentation.
YAML to JSON Converter
Server-side conversion via PHP's native YAML extension with Spyc as fallback. Handles multi-document YAML (--- separators): a Kubernetes manifest with Deployment, Service, and ConfigMap returns each document as an element in a JSON array. Accepts .yaml/.yml file upload up to 1 MB.
Tip: Convert a Kubernetes manifest to JSON and paste it into the JSON Formatter to catch nesting issues before kubectl apply.
XML Formatter & Validator
Format, minify, or validate XML using the browser's native DOMParser — no library, no server. Parse errors come back in plain English ("Attribute is missing a value") rather than raw browser exception messages. Works on SOAP responses, Maven configs, RSS feeds, and Spring XML contexts.
Tip: DOMParser makes implicit namespaces explicit in output. Extra xmlns: declarations you didn't write were already in the document; the formatter surfaced them.
CSS, Markdown & HTML
CSS Formatter + Validator
Format, minify, or validate CSS. Beautifies minified stylesheets with readable indentation, or compresses CSS for production. Syntax errors show the exact line and column. Server-side, nothing stored.
Tip: Minify your final stylesheet and compare byte counts — an unoptimised CSS file often drops 30–40% after compression.
Markdown to HTML Converter
Live split-panel preview: Markdown on the left, rendered HTML on the right. Uses marked.js with CommonMark and GitHub Flavored Markdown — tables, task lists, fenced code blocks, strikethrough all supported. Raw HTML tab for copying output directly into a CMS or API call.
Tip: Enable GFM mode if your Markdown has GitHub-style task list checkboxes (- [ ]). They render to actual <input type="checkbox"> elements.
HTML Entity Encoder / Decoder
Encode HTML special characters to named entities (< → <) or numeric entities for all non-ASCII characters. Decode any entity notation — named, numeric decimal, or numeric hex. Output updates as you type; no button click required.
Tip: The encoder always processes & before < and > to prevent double-encoding on a second pass.
Encoding & Number Formats
Base64 Encoder / Decoder
Encode text, files, or URLs to Base64 or URL-safe Base64. Decode Base64 back to text, images, or binary with hex dump. Runs entirely in-browser — useful for generating data URIs or inspecting encoded attachments without uploading the file anywhere.
Tip: Use URL-safe mode for JWT custom claims or query string values — it replaces + with - and / with _, both safe in URLs without percent-encoding.
URL Encoder / Decoder
Three modes: encodeURIComponent for query string values, encodeURI for full URLs that preserve :// and /, and a full URL decode that processes every %xx sequence at once. Live output, with error detection for malformed percent sequences.
Tip: Use encodeURIComponent for individual parameter values and encodeURI for complete URLs — mixing them is a common source of double-encoding bugs.
Binary Translator
Convert text, decimal, or hex to binary — and back. Three modes, bidirectional. Runs entirely in-browser. Useful for debugging data format issues and explaining binary representations.
Tip: Switch to hex mode to convert between binary and hexadecimal directly, avoiding the two-step decimal intermediary.
Number Base Converter
Convert numbers between binary, octal, decimal, and hexadecimal with live updates. Supports BigInt for 64-bit values, two's complement with 8/16/32/64-bit width selector, prefix display (0x, 0b, 0o), and nibble/byte grouping.
Tip: Enable two's complement to see the negative decimal value for a given bit pattern at any bit width — useful when debugging signed integer representations.
Case Converter
Converts text between 12 case formats in real time: snake_case, camelCase, kebab-case, PascalCase, Title Case, CONSTANT_CASE, dot.case, path/case, sentence case, lower case, UPPER CASE, and alternating case. Fully browser-side.
Tip: snake_case → camelCase is the fastest way to translate Python-style API field names to JavaScript property names.
Dates, Time & Scheduling
Unix Timestamp Converter
Convert Unix epoch timestamps to readable dates and back. Auto-detects seconds vs. milliseconds (threshold: 1e12, which correctly handles 13-digit millisecond values). Shows UTC, local, ISO 8601, and relative time ("3 hours ago"). Live clock updates every second.
Tip: Paste a millisecond timestamp directly — no manual toggle needed. The auto-detect threshold handles it.
Timezone Converter
Convert any time between two IANA timezones using a searchable 175-zone combobox. Shows UTC offset delta, ISO 8601 copy value, and handles half-hour offsets (India UTC+5:30, Nepal UTC+5:45) and DST spring-forward gaps correctly.
Tip: The swap button reverses source and target zones without retyping — quicker when coordinating across two locations.
Cron Expression Builder
Build cron expressions visually with a five-field editor, or paste an expression to parse it into plain English ("At 09:00 on weekdays"). Seven preset chips, and a next-5-fires panel with UTC/local toggle.
Tip: Parse mode decodes legacy cron jobs from inherited scripts — paste the expression and see exactly what it schedules before touching anything.
Auth, Security & Tokens
JWT Decoder
Paste any JSON Web Token and see the header (algorithm, key ID) and payload (all claims) as formatted JSON. Timestamp claims (exp, iat, nbf) convert from Unix epoch to readable UTC with expired/valid status labels. Nothing stored or logged.
Tip: Check exp first when debugging a 401. If the token is expired, that answers the question before checking algorithm mismatches or audience claims.
UUID Generator
Generate UUID v4 (random), v1 (time-based), v7 (time-ordered), or Nil UUIDs. Up to 100 at once. Uses window.crypto.getRandomValues(). Copy all with one click.
Tip: UUID v7 is time-ordered like v1 but uses a random node component — better for database primary keys because it avoids leaking MAC address information.
Hash Generator
Generates MD5, SHA-1, SHA-256, and SHA-512 hashes simultaneously from text or files. All four algorithms run in-browser via SubtleCrypto and spark-md5 — nothing is uploaded. File mode handles up to 20 MB via the FileReader API.
Tip: File hashing is the fastest way to verify a download against a published checksum — paste the vendor's SHA-256 and compare it to the result here.
Password Generator
Generates cryptographically secure passwords using window.crypto.getRandomValues(). Set length and character types (uppercase, lowercase, digits, symbols). Entropy meter reflects the strength of the current configuration.
Tip: The entropy score drops sharply when symbols are excluded at short lengths — keep symbols on for passwords under 20 characters.
Color & Design
Color Picker
Pick any color from a visual wheel and get the HEX, RGB, and HSL codes. Copy any format with one click. Fully in-browser.
Tip: HSL is often more useful when adjusting a brand color — tweak the L (lightness) value while keeping hue and saturation fixed to create tints and shades.
Hex to RGB Color Converter
Convert HEX to RGB, RGB to HEX, and HEX/RGB to HSL. All three formats update live as you type in any field. Accepts 3-digit shorthand HEX (#fff, #09f) and expands to 6-digit before converting.
Tip: Type in any field to drive the conversion — you don't have to start from HEX.
QR Codes & Links
QR Code Generator
Generate QR codes from URLs, plain text, WiFi credentials, or vCard contacts. Download as PNG or SVG. Four error correction levels (L through H). SVG output scales to any print size without quality loss.
Tip: Use Level H error correction if you plan to overlay a logo on the QR code center — it recovers up to 30% of damaged data, keeping the code scannable despite the overlay.
QR Code Reader
Decode any QR code from an uploaded image or live camera scan. Uses jsQR, which runs entirely in-browser — nothing uploaded or stored. Detects URLs and renders them as clickable links.
Tip: Works with QR codes embedded in screenshots — export a PDF page as PNG and upload it directly.
URL Shortener
Shortens any URL to at-use.com/r/{code} using a 6-character alphanumeric code. Permanent 301 redirect that passes link equity. The same URL submitted twice returns the same short code rather than creating a duplicate. Includes QR code output.
Tip: 301 redirects pass SEO link equity through to the destination — your short link doesn't dilute the value of inbound links.
Code & Text
Code to Image Converter
Converts code snippets to styled PNG or JPEG images. 8 themes, 40+ language highlighters, configurable padding and font size. No watermark. Useful for sharing code in social posts or slides where monospace formatting breaks down.
Tip: Export at 2× scale for Retina/HiDPI displays — the text stays sharp at any rendered size.
Regex Tester
Test regular expressions against input text with match highlighting. Supports flags (global, case-insensitive, multiline, dotAll). Shows match count, match positions, and group captures. Runs in-browser.
Tip: Enable the dotAll (s) flag to match patterns that span newlines — without it, . stops at line breaks.
Text Diff
Compare two blocks of text side by side with word-level or character-level diff — additions in green, deletions in red. No line limit. Useful when the inputs are prose or config files rather than structured JSON (for structured JSON comparison, use JSON Diff Checker, which handles key-order and semantic equivalence). Runs entirely in the browser.
Tip: Character mode surfaces one-character changes — a swapped punctuation mark, a case flip — that word mode collapses into a whole-word replacement.
Word Counter
Counts words, characters, sentences, and paragraphs instantly. Shows estimated reading time and top-5 keyword frequency. Live update as you type, no submit button.
Tip: The keyword frequency list spots overused words in a draft — paste any block of text and the top-5 shows repetition patterns in seconds.
What's next
These 29 tools cover the daily friction of developer work: format checks, conversions, quick lookups, and the small tasks that shouldn't take five minutes but somehow do. All free, no account, no expiry.
The pipeline is active and new tools ship weekly. If there's something you reach for regularly that isn't here, let us know.