26 Free Online Developer Tools - No Signup, No Install (2026)
Every developer has a graveyard of browser bookmarks for tools used once every few months: a JWT decoder, a cron expression validator, a DNS checker. The problem with most of these tools is they require creating an account, installing an extension, or pasting data into a site that could be logging everything you send.
I have been using at-use.com as my go-to bookmark for exactly this reason. It is a collection of 30+ browser-based tools that run in the browser or server-side (for network lookups), no account required. Here is a rundown of the ones I actually use.
Encoding & Decoding
Base64 Encoder/Decoder
Paste in text or a binary string, get Base64 out. Or the reverse. Handles URL-safe Base64 variants too. Useful for decoding config file values, JWT payloads, or any API response that came back encoded.
URL Encoder/Decoder
Encodes special characters for query strings or decodes a percent-encoded URL into something readable. Faster than decodeURIComponent() in the browser console when you are debugging a broken redirect.
HTML Entity Encoder
Two modes: HTML-safe (encodes <, >, &, ", ') and all-non-ASCII (encodes every character above codepoint 127). Useful when you need to embed user-generated content in HTML without running a full sanitization library.
Binary Translator
Converts text to binary and back. Also handles hex and decimal. The BigInt implementation handles 64-bit values without precision loss, which matters when debugging numeric IDs from databases that use bigint columns.
Text & Code
JSON Formatter
Paste in minified JSON, get pretty-printed output with syntax highlighting. Validates and shows the exact line/character of any parse errors. I use this constantly when logging API responses as single-line strings.
Markdown to HTML
Live split-panel preview. Renders GFM: tables, task lists, fenced code blocks, strikethrough. Outputs clean HTML you can copy or download as a .html file.
Text Diff
Paste two versions of a string and see a character-level diff. Useful when you need to spot the difference between two similar error messages or config values without setting up a full diff tool.
Case Converter
camelCase to snake_case to PascalCase to kebab-case to SCREAMING_SNAKE_CASE. Handles Unicode correctly, not just ASCII.
Regex Tester
Live regex testing with match highlighting. Supports flags (global, case-insensitive, multiline, dotAll). Shows match groups and capture groups separately.
Readability Checker
Runs Flesch-Kincaid, Gunning Fog, and a few other readability scores against a block of text. Useful for technical writing - especially when checking that documentation is at the right reading level.
Security & Authentication
JWT Decoder
Paste in a JWT, get the header and payload decoded. No verification (client-side decoder, not a validator), but useful for inspecting token contents during debugging without sharing the token with any external service.
Hash Generator
MD5, SHA-1, SHA-256, SHA-512. Paste text, get the hash. Good for quickly verifying checksums or confirming that two strings produce the same hash.
Password Generator
Configurable length, character sets (uppercase, lowercase, numbers, symbols), excludes ambiguous characters by default. All generation happens client-side.
Time, Date & Scheduling
Unix Timestamp Converter
Converts between Unix timestamps and human-readable dates. Handles milliseconds. Shows results in multiple timezones simultaneously - useful when looking at API logs that store timestamps in UTC while you are somewhere else.
Cron Expression Builder
Visual builder for cron expressions: click through minute/hour/day/month/weekday fields. Includes a parser that takes any cron expression and outputs a plain-English description. Shows next 5 scheduled run times with UTC/Local toggle.
Network & DNS
DNS Lookup
A/AAAA/CNAME/MX/TXT/NS records for any domain. Server-side lookup, so you see what is actually propagated, not what is cached on your local resolver.
WHOIS Lookup
Full WHOIS data for any domain. Useful for checking registration dates, nameserver assignments, or registrar details.
CNAME Lookup
Resolves CNAME chains end-to-end. Helpful when debugging CDN configurations or alias records that chain through multiple levels.
MX Lookup
Lists MX records with priorities. Good for checking email routing or verifying that custom domain email is correctly pointed.
SPF & DMARC Checker
Parses SPF records and DMARC policies, flags common misconfigurations (overly broad +all, missing p=reject in DMARC). Practical for debugging deliverability issues.
SSL Checker
Shows certificate chain, expiry dates, issuer, and Subject Alternative Names. Flags common issues like mismatched common name or incomplete chain. Useful before deploying a cert or checking a third-party domain.
HTTP Headers Checker
Fetches and displays response headers for any URL. Shows redirect chains up to 5 hops. Highlights security headers - HSTS, CSP, X-Frame-Options, X-Content-Type-Options - and flags which are missing.
Online Status Checker
Checks if a URL is reachable from the server, bypassing your local network. Useful when unsure if a service is down for everyone or just your connection.
Generators & Utilities
UUID Generator
Generates UUID v4 (random). Client-side, uses crypto.randomUUID(). Generates a batch at once if you need multiple.
Number Base Converter
Converts between binary, decimal, hex, and octal. Uses BigInt for 64-bit values. Includes a two's complement viewer with configurable bit width (8/16/32/64-bit) for debugging signed integer representations.
Code to Image
Takes a block of code and renders it as a shareable PNG with syntax highlighting and a clean background. Useful for documentation, presentations, or posts where you want to show a code snippet without a raw screenshot.
JSON Diff Checker
Paste two JSON objects and see exactly what changed - additions highlighted in green, removals in red, with side-by-side and unified diff modes. Supports key-order sensitivity toggle and hiding unchanged content. Server-side processing, 1 MB per pane limit.
Color Picker from Image
Upload any image and click anywhere on it to extract the exact HEX, RGB, and HSL color codes at that pixel. Useful for pulling brand colors from logos or screenshots without loading a full design tool.
Text Diff Checker
Line-by-line comparison of two text blocks. Returns a unified diff with added/removed/unchanged stats and similarity percentage. Handles large pastes without client-side memory limits.
Unix Timestamp Converter
Bidirectional epoch time conversion - paste a 10-digit (seconds) or 13-digit (milliseconds) timestamp to get a human-readable date, or enter a date to get the epoch. Auto-detects seconds vs milliseconds.
What is missing
No API testing interface, no SQL formatter, no container tooling. Now at 30 tools. For standalone lookup and conversion tasks it covers the common ground well, without requiring an account or sending your data to a third party.
The developer tools hub groups everything above in one place. The network DNS hub has the full set of network tools.
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