OneTaskFree Online Developer Tools
JSON Formatter, Cron Generator, Regex Tester, Hash Generator and JWT Decoder
The small jobs that interrupt real work: checking a regex, working out what a cron line actually does, formatting a minified file, decoding a token, or generating the structured data a page needs before it ships. Each one is a single page here, grouped by the kind of job, and none of them sends your data anywhere.
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CVE ID Validator
Check a list of CVE IDs for format errors and duplicates.
CVE ID Validator
Check a list of CVE IDs for format errors and duplicates.
IP Address Info
Classify any IPv4 or IPv6 address and see its every form.
IP Address Info
Classify any IPv4 or IPv6 address and see its every form.
NTLM Hash Generator
Windows NTLM and LM hashes of a password, computed in your browser.
Unicode Confusables Detector
Find lookalike and invisible Unicode characters hiding in text.
Dev Utilities 13
Regex, cron, chmod, git, semver, epoch, subnets, DNS and other daily helpers.
CHMOD Calculator
Convert Unix permissions between rwx, octal and symbolic.
CSS Selector Tester
Test a CSS selector against pasted HTML and list every matching element.
Core Web Vitals Calculator
Check whether your page passes Core Web Vitals and which metric to fix first.
DNS Lookup
Query any DNS record for a domain with TTLs and explanations.
HTTP Status Codes
Look up what any HTTP status code actually means.
IP Address Info
Classify any IPv4 or IPv6 address and see its every form.
Image Size Calculator
Estimate image file size and see how oversized it is for its slot.
Keycode Tester
Press a key and see exactly what your browser reports.
Regex Generator
Build a regex from a preset or from sample strings, ready to paste.
SemVer Tool
Sort, compare and bump semantic version numbers.
What Is My IP
See the public IP address every website sees when you connect.
Base Converter
Convert numbers between binary, octal, decimal and hex.
CURL Converter
Turn a curl command into code in 24 languages.
Formatters & Validators 2
Beautify and minify JS, CSS and HTML; validate markup, SVG, URLs and emails.
Data & Encoding 3
CSV, JSON, YAML, XML and SQL formatters; Base64, URL, hex and string escaping.
Security & Identifiers 21
Hashes, HMAC, bcrypt, JWT decoding, password and UUID generation and validation.
AES Key Generator
Random AES-128, 192 or 256-bit keys in hex, Base64 or JWK.
Bearer Token Decoder
Decode an Authorization header and find out what kind of token it is.
CRC32 Calculator
CRC-32, CRC-32C and Adler-32 checksums of text or hex bytes.
CVE ID Validator
Check a list of CVE IDs for format errors and duplicates.
Hex Dump Viewer
View any file as hex and ASCII, with type detection and entropy.
Memorable Password Generator
Random words, a symbol and digits — strong, and you can remember it.
NTLM Hash Generator
Windows NTLM and LM hashes of a password, computed in your browser.
Passphrase Generator
Diceware passphrases from the EFF wordlist, generated locally.
Password Policy Generator
Write a modern NIST-based password policy for your organisation.
Random PIN Generator
Random 4, 6 or 8 digit PINs, avoiding 1234 and 0000.
Random String Generator
Cryptographically random strings in any length and character set.
SSH Key Fingerprint
Get ssh-keygen style SHA256 and MD5 fingerprints from any public key.
Secret Scanner
Find leaked API keys, tokens and passwords in pasted code.
Signature Verifier
Check whether a signature over a message matches a public key.
TOTP QR Code Generator
Authenticator app setup QR codes from a secret, issuer and account.
UUID Generator
Random v4 or time-ordered v7 UUIDs, generated in your browser.
UUID Validator
Check a list of UUIDs and decode their version, variant and timestamp.
Unicode Confusables Detector
Find lookalike and invisible Unicode characters hiding in text.
WiFi Password Generator
WPA2/WPA3 keys with no look-alike characters, easy to read aloud.
IP Range To CIDR Converter
Turn start and end IP addresses into the fewest CIDR blocks.
SSH Key Converter
Convert SSH public keys between OpenSSH, SSH2 and PEM formats.
SEO 9
Structured data, meta tags, previews, robots, sitemaps, redirects and page audits.
Hreflang Generator
Generate hreflang link tags, headers or sitemap XML for multilingual pages.
Local Business Schema Generator
Build LocalBusiness JSON-LD with address, geo, opening hours and social profiles.
Meta Description Generator
Draft meta descriptions from your own page text, trimmed to length.
Redirect Generator
Turn an old-to-new URL list into 301 rules for Apache, Nginx, Netlify and Vercel.
Robots.txt Checker
Check a robots.txt file line by line before you deploy it.
Sitemap Validator
Validate sitemap.xml and sitemap index files against the sitemaps.org protocol.
Title Length Checker
Check page titles and meta descriptions by pixel width, not just characters.
UTM Campaign URL Builder
Build correctly encoded UTM campaign links with consistent naming.
WCAG Checker
Find WCAG accessibility failures in pasted HTML, with the criterion each breaks.
Accessibility 3
Simulate, generate and check the things that make a page usable by everyone.
AI 1
Tokens, API costs, context windows, prompts and cleaning model output.
How the developer tools are organised
Dev Utilities is the everyday shelf. Regex testing and generation, cron and chmod, common git commands, semantic version comparison, epoch and number-base conversion, HTTP status codes, keyboard key codes, user-agent parsing, cURL to code, URL query parsing, IP subnetting and DNS record lookup.
Formatters & Validators takes a file and either tidies it or tells you what is wrong with it: JavaScript, CSS and HTML formatting; CSS, HTML and SVG validation; URL and email address validation against the actual specifications rather than a rough pattern.
Data & Encoding is for structured text and the representations it passes through: CSV to JSON and back, CSV column selection, JSON, YAML, XML and SQL formatting, JSON to YAML and XML to JSON conversion, Base64, URL encoding, hex, string escaping for source code and HTML entities.
Security & Identifiers covers hashing (MD5 through SHA-512), HMAC signing, bcrypt hashing and verification, JWT decoding, strong password generation, and UUID generation and validation.
SEO is the largest group: schema generators for articles, breadcrumbs, FAQs, local businesses and products; a schema validator; canonical and hreflang generators; meta description and title length tools; a SERP preview and a Twitter card preview; robots.txt and sitemap checking; redirect rules; heading structure, internal link and WCAG checks.
Why client-side matters here more than anywhere
Developer tools are where the most sensitive strings end up being pasted: bearer tokens, connection strings, a config file with a secret in it, a production log line. A hosted tool that sends that to its own server has just leaked it, whatever its privacy policy says. Every page in this section runs in your browser and makes no network request with your input. Hashing uses the Web Crypto API, formatting and parsing are pure JavaScript, and the SEO tools generate their output locally — the only thing that leaves your machine is what you choose to copy.
Accuracy over convenience
Where a tool implements a specification — cron syntax, semver precedence, RFC 5322 addresses, JSON-LD vocabulary — it follows the specification rather than a simplified approximation, and says so on the page. Where a convention varies between systems (which fields a UUID version carries, how a shell escapes a string), the tool states the convention it is using so the output can be trusted in the place you are about to paste it.
FAQ
Is my data sent to a server by any of these tools?
No. Encoding, formatting, hashing and subnet maths all run in JavaScript on your device. Nothing you paste leaves your machine, so decoding a real token or formatting a real config file is safe.
Can I decode a hash back to the original value?
No. Hashing is a one-way function — the input cannot be recovered from the digest. Services that appear to reverse a hash are looking the value up in a precomputed table of common inputs, which is exactly why passwords should be salted.
Is Base64 a form of encryption?
No. Base64 is a reversible encoding designed to move binary data through text channels. Anyone can decode it in seconds, so it provides no confidentiality at all.
Do these tools work offline?
Once a page has loaded, yes. The logic ships with the page, so the tool keeps working if your connection drops. Reloading the page requires a connection unless your browser has cached it.
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Everyday maths, loans, dates, health and DIY. Nothing uploaded.
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Units, images, audio, video, documents and code formats, converted in your browser.
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Writing, lists, Markdown, HTML, Morse and ciphers.
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Layouts, effects, shapes, components, forms and colour. Live preview.
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Random names for people, fantasy races, sci-fi worlds and RPG characters.
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Sourced, dated reference tables you can search, cite and download.
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Pay, bills and property calculators that show their working.
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Calendar lookups, date arithmetic and live countdowns to the days that matter.
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Fractions, primes, algebra and statistics, with the working shown.
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Physics, chemistry and electronics calculators, with the formula shown.
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Word Games
Scrabble, Wordle, anagrams, crosswords and rhymes, solved.
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