Developer Tools
Format, validate and encode the data you work with.
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The utilities you reach for a dozen times a day — a JSON formatter that tells you exactly where the syntax broke, Base64 and URL codecs, and a timestamp converter. The formatters, encoders and converters run entirely in the page, so it is safe to paste production payloads into them. The three network checkers — the SSL certificate checker, the email address validator's MX lookup and the Open Graph preview — have to reach another server, and each one says exactly what it sends.
Most used
All 21 Developer Tools
21 tools
JSON FormatterPretty-print or minify JSON, with the exact error position.JSON ValidatorCheck JSON syntax and get a plain-English explanation of errors.JSON to CSVFlatten nested JSON into a spreadsheet-ready CSV.Base64 EncoderEncode text or a file to Base64, standard or URL-safe.Base64 DecoderDecode Base64 back to text or download it as a file.URL EncoderPercent-encode a whole URL or a single query parameter.URL DecoderDecode percent-encoded URLs and break out query parameters.HTML FormatterIndent messy HTML, or minify it for production.CSS FormatterBeautify or minify stylesheets, including nested rules.Timestamp ConverterUnix time to a readable date, in UTC and your local zone.File Checksum VerifierCalculate MD5, SHA-1, SHA-256 or SHA-512 and compare with a published hash.SSL Certificate CheckerSee when a domain's SSL certificate expires and whether its chain is trusted.Email Address ValidatorCheck email address format with plain-English errors, typo fixes and MX lookups.Password Strength CheckerEstimate how long a password would take to crack, checked privately in your browser.Open Graph PreviewPreview how a link looks when shared, and check or write its Open Graph tags.CSV to JSONTurn CSV or a spreadsheet export into a JSON array of objects.JWT DecoderRead a JSON Web Token's header, payload and expiry — decoded, not verified.Hash GeneratorMD5, SHA-1, SHA-256 and SHA-512 hashes and HMACs of any text.Cron Expression ExplainerTranslate a cron schedule into plain English and list its next run times.Regex TesterTest a JavaScript regular expression with live match highlighting and groups.Markdown to HTMLConvert Markdown to clean HTML with a live preview.
What runs in your browser, and what does not
Developers paste sensitive things into tools like these: API responses, tokens, customer records. So the first thing to know about each tool is where the data goes. Twelve of the tools above run entirely in the page. Three have to contact another server, and they say so.
Formatting and validating
The JSON Formatter pretty-prints or minifies and reports a syntax error with its exact line and column, and the JSON Validator explains the error in plain words with a likely cause. JSON to CSV flattens nested objects into dotted column names and builds the column list from every record, so uneven data does not lose fields. The HTML Formatter and CSS Formatter indent or minify markup and stylesheets.
Encoding and decoding
The Base64 Encoder and Base64 Decoder handle text and files, including URL-safe output and data URIs. Base64 is an encoding, not encryption: anyone can reverse it, so it hides nothing. The URL Encoder and URL Decoder percent-encode a whole address or a single parameter value — a distinction that matters, because the two need different characters escaped. The Timestamp Converter shows a Unix timestamp in UTC and your local time together, since the gap between them is where date bugs come from.
Verifying
The File Checksum Verifier calculates MD5, SHA-1, SHA-256 or SHA-512 for a download and compares it with the published hash. It reads the file in chunks on your device, so even a disk image is never uploaded. Prefer SHA-256 where the publisher offers it; MD5 and SHA-1 catch accidental corruption but not deliberate tampering. The Password Strength Checker estimates how quickly a password could be guessed, on your device.
The three network checkers
A web page is not allowed to read another site's certificate, mail records or HTML, so these three are carried out by this site's server:
- The SSL Certificate Checker connects to the domain you enter and reads its certificate and chain.
- The Email Address Validator checks the format in your browser; its mail server lookup sends only the domain name, never the full address.
- The Open Graph Preview fetches the head of the page you enter to read its sharing tags.
The certificate checker and the preview fetcher accept only public internet addresses, and each page states exactly what is sent. One limit applies to the email validator in particular: no tool can prove a mailbox exists without sending it a message, so the check stops at format and domain.
Guides
- How to create a strong password you can actually useWhy length beats symbols, what makes passwords easy to crack, when to use a passphrase, and how to generate and check strong passwords safely.
- UTM parameters explained: how to see which links bring you visitorsWhat utm_source, utm_medium and utm_campaign do, how to name them consistently, where the results appear, and the mistakes that corrupt your data.
- How to verify a file checksum (SHA-256) — and what it provesCheck that a download is exactly what its publisher released: find the checksum, compare it in your browser or from the command line, and understand its limits.
- How to fix invalid JSON: the common errors and what they meanTrailing commas, single quotes, comments, unescaped characters and the other mistakes that make JSON invalid — with examples and how to find the exact line.
- Unix timestamps explained: seconds, milliseconds and time zonesWhat a Unix timestamp is, how to tell seconds from milliseconds, why dates come out a day wrong, and the year 2038 problem — with examples you can check.
- How to fix link previews: Open Graph tags explainedWhy a shared link shows the wrong image, no image or an old title, which Open Graph tags fix it, the right image size, and how to make platforms refresh the preview.
- How to write a robots.txt file — with examplesWhat robots.txt can and cannot do, how the rules are matched, examples for common cases including AI crawlers, and the mistakes that hide a site from search.
- How to schedule a meeting across time zones without mistakesFind hours that suit people in several countries, avoid the daylight saving weeks that move meetings, and write invites nobody can misread.
- What is Base64, and when should you use it?How Base64 turns any data into plain text, why it makes things a third bigger, where it is used — data URIs, email, tokens — and why it is not encryption.
- URL encoding explained: what %20 means and when to encodeWhy web addresses contain %20 and %C3%A9, which characters must be encoded, the difference between encoding a whole URL and a single value, and %20 versus +.
- How to check when an SSL certificate expires — and why it mattersSee when a site's HTTPS certificate expires, spot chain problems browsers hide, and keep automatic renewal from failing silently as lifetimes get shorter.
- How to check an email address is valid before you sendCatch typos and badly formed email addresses, check that a domain can receive mail, clean a list in bulk, and understand what validation cannot prove.
- What is a UUID — and should you use version 4 or version 7?How UUIDs identify things without a central counter, how to read one, why collisions are not a practical worry, and which version to use for database keys.
- Structured data for beginners: FAQ and Product schemaWhat schema markup is, what FAQ and Product structured data can and cannot do for search results today, and how to add JSON-LD to a page correctly.
- EST vs EDT, GMT vs UTC: time zone abbreviations explainedEST is not the same as EDT, and GMT is not quite UTC. What common time zone abbreviations mean, when daylight saving changes them, and how to avoid missed calls.
- How to convert curly quotes to straight quotesSmart quotes from Word and Docs break code, CSV files, passwords and search. How to straighten them, plus em dashes and ellipses, and how to stop them being added.
- How long would it take to crack my password?From seconds to millions of years, depending on length, randomness and how a site stores it. Worked examples, why patterns ruin estimates, and a safe check.
- A strong Wi-Fi password that is still easy to typeWi-Fi passwords get typed on TVs, consoles and guests' phones. How to make one that is long and strong but painless to enter, and how to share it with a QR code.
- How to open a JSON file in ExcelTwo ways to get JSON data into a spreadsheet: Excel's Power Query import, or converting to CSV first. How nested data is flattened and how to avoid broken numbers.
- The year 2038 problem explainedOn 19 January 2038, 32-bit Unix time runs out and some systems will jump back to 1901. What exactly happens, what is affected, and how to check your own software.
- ISO 8601 date format explained (YYYY-MM-DD and beyond)2026-10-03T14:30:00Z decoded: the international date and time format, time zones and offsets, week numbers and durations, and why it is the safest format to use.
- How to embed an image in HTML or CSS with a Base64 data URIA data URI puts an image directly inside HTML, CSS or JSON. How to make one, the 33% size cost, where it helps, and why it often fails in emails.
- How to decode a JWT and read its claimsA JWT is three Base64URL parts separated by dots. How to read the header and payload, what the common claims mean, and why decoding is not the same as verifying.
- URL query parameters explained: what comes after the ?How to read the part of a web address after the question mark: keys and values, ampersands, fragments, encoding and tracking tags, and what not to put in a URL.
- How to fix an incomplete SSL certificate chainYour site works in a browser but apps, scripts and some phones report certificate errors. Usually the intermediate certificate is missing. How to check and fix it.
- SSL certificates are getting shorter lifetimes: what changes for youPublic TLS certificates are moving from about a year to 200 days, then 100, then 47 by 2029. The schedule, why it is happening, and how to make renewals automatic.
- How to check a domain's MX records (can it receive email?)MX records say which servers accept email for a domain. How to look them up, read priorities, spot null MX and missing records, and fix email after a move.
- How long should a meta description be?Google cuts descriptions by pixel width, about 150 to 160 characters on desktop. How to write one that fits, why Google rewrites it, and what it does for clicks.
- “Unexpected token < in JSON at position 0”: what it means and how to fix itThis error means your code expected JSON but got HTML, usually an error page or a login redirect. How to see what really came back and fix the cause.
- Why text shows ’, é or � instead of apostrophes and accentsGarbled characters like ’ and é appear when UTF-8 text is read with the wrong encoding. What causes it, how to fix the file, and how to stop it recurring.
- Why a CSV file opens in one column in Excel — and how to fix itEverything lands in column A when Excel expects a different separator. Why commas and semicolons clash between regions, and three ways to split it properly.
- How to stop Excel turning numbers into dates and dropping leading zerosExcel turns 1-2 into 1 Feb, 00042 into 42 and long IDs into 1.23E+15. Why it guesses, which changes cannot be undone, and how to import a CSV as text.
- Why a site shows a certificate name error on www or without itA certificate covering example.com but not www.example.com (or the reverse) triggers a browser warning. How to confirm which names are covered and fix it.
- Why a link breaks when you paste it into an email, chat or documentPasted links fail when trailing punctuation, spaces, line wraps or unencoded characters change the address. How to spot the cause and share links that work.
- Why a website rejects your strong passwordLong random passwords can still fail a site's rules: maximum lengths, banned symbols, required character types or breach checks. How to find the rule.
- Why formatting or minifying HTML changed how the page looksWhitespace between inline elements renders as a space, so reformatting HTML can add gaps between buttons or images. Why, and how to make layout robust.
- Why your CSS isn’t being applied: a checklistA style that does nothing is usually overridden, mistyped, not loaded, cached or cut off by a missing brace. How to find which, using browser tools.
- Why an email bounces even though the address looks validA correctly formatted address can still bounce: the mailbox may not exist, be full, or reject your server. How to read the bounce and what to check.
- Why visits from your UTM links show up as direct or unassignedTagged links land in Direct or Unassigned when redirects strip tags, values are inconsistent, tags sit after # or analytics never loads. How to fix it.