Free developer tools
JSON, base64, hashes and HMAC, JWT and certificate decoding, regex, cron, UUIDs, subnets, timestamps, curl conversion and fake data. All client-side, so a secret you paste stays on your machine.
- Prompt Analyzer — Paste an LLM system prompt and one AI pass scores it 1–5 across eight dimensions — purpose coherence, context-vs-instruction harmony, spikiness, shoutiness, contradictions, framing, an escape hatch and downstream stakes — as a heatmap spider chart, with concrete issues listed. Then answer the gaps and get a rewritten, stronger prompt. Three analyses per 24 hours.
- Regex Tester — Write a regular expression and see every match highlighted in your test text as you type, with capture groups and a live match count. Uses the native JavaScript engine, entirely in your browser — nothing is uploaded.
- JWT Decoder — Paste a JSON Web Token to decode its header and payload into readable JSON, with expiry and issued-at times shown in local time. Decoding happens entirely in your browser — the token is never uploaded and the signature is not verified.
- Cron Explainer — Paste a 5-field cron expression and get a plain-language description of when it runs, plus the next several run times in your local timezone. Supports ranges, steps and lists, computed in your browser.
- Text Diff — Paste two versions of a text and see a line-by-line diff — additions, removals and unchanged lines colour-coded, with a count of what changed. Runs entirely in your browser; nothing is uploaded.
- Unix Timestamp — Convert a Unix timestamp (seconds or milliseconds) to a readable date and back, in both your local timezone and UTC, with a live current-time readout. Runs entirely in your browser.
- Number Base Converter — Convert a number between binary, octal, decimal, hexadecimal and any base from 2 to 36, all at once and in real time. Arbitrary-precision, so large values stay exact. Runs entirely in your browser.
- IP Subnet Calculator — Enter an IPv4 address with a CIDR prefix (e.g. 192.168.1.10/24) to get the network and broadcast addresses, the usable host range, the subnet mask and wildcard, and the number of usable hosts. Runs entirely in your browser.
- .gitignore Generator — Pick the languages, tools and editors you use and get a combined .gitignore with the usual build artefacts, dependency folders and OS/editor cruft — ready to copy or download. Runs entirely in your browser.
- JSON to TypeScript — Paste a JSON object or array and get clean TypeScript interfaces inferred from it — nested objects become their own interfaces, arrays are typed, and keys missing from some items become optional. Runs entirely in your browser.
- README Generator — Fill in your project’s name, description, features, install and usage steps and licence to generate a clean, well-structured README.md — with a live preview of the Markdown — ready to copy or download. Runs entirely in your browser.
- Markdown Table Generator — Paste comma- or tab-separated data (copied straight from a spreadsheet works) and get a neatly padded GitHub-flavoured Markdown table, with a choice of column alignment. Runs entirely in your browser.
- SVG Editor — Paste or drop an SVG, see it render live, and copy or download a cleaned-up version. The built-in optimiser (SVGOMG-style, sane defaults) strips editor cruft — comments, metadata, Inkscape/Illustrator namespaces — collapses whitespace and rounds coordinates so your icons ship lean. Runs entirely in your browser; nothing is uploaded.
- Fake Data Generator — Generate realistic-looking sample records — names, emails, phones, cities, companies, dates and IDs — for seeding tests, mockups and demos. Pick the fields and count, then export as JSON or CSV. Runs entirely in your browser.
- UUID Generator — Generate one or many RFC-4122 v4 UUIDs with optional formatting, entirely in your browser.
- Code Formatter — Format, minify and validate code in your browser — JSON (line/column errors, sort keys) plus CSS and XML beautify/minify. Nothing uploaded.
- Base64 Convert — Encode and decode Base64 text with full UTF-8 support and a URL-safe option — entirely in your browser.
- CSV Merge & Join — Match two CSV exports on a column they share — an id, an email, an order number — and get one file with both sides’ data, told how many rows matched and how many found nothing. Or stack two files aligned by column NAME rather than position, because positional stacking silently moves a phone number into the city column.
- JSON Diff — A line diff on JSON is close to useless: reformatting makes every line look changed while the data is identical. This compares values by path and lists exactly what was added, removed or changed, with an option to treat arrays as unordered.
- cURL Converter — Copy a request as cURL from your browser’s network tab and paste it here to get the same request as fetch, Node, axios, Python requests or HTTPie. Quoting, line continuations, multiple headers and JSON bodies are handled properly, and nothing leaves the page.
- CSV Cleaner — Clean up a CSV without opening a spreadsheet — trim stray spaces, drop blank rows and entirely empty columns, and remove duplicate rows. It detects the separator itself and flags rows whose field count does not match the header, which is what usually breaks an import.
- HMAC Generator — Compute an HMAC over any message with a shared secret — SHA-256, SHA-1, SHA-384 or SHA-512, key as text, hex or base64, output as hex or base64. Paste the value you were sent and it tells you whether it matches, which is what you need when debugging a webhook signature.
- Cron Builder — Build a cron expression without remembering the field order — choose daily, weekly, monthly or every few minutes. It lists the next five times the schedule would actually fire, and warns about the day-of-month and day-of-week trap where cron fires when either matches.
- Certificate Decoder — Paste a PEM certificate and read what is actually in it: who it was issued to and by, when it expires and in how many days, the key and signature algorithms, every hostname it covers, its extensions and its SHA-256 fingerprint. Decoded in your browser by a small ASN.1 parser — nothing is uploaded, and no online checker sees your certificate.
- Email Header Analyser — Paste the raw headers of an email and see the route it actually took, with the delay at each hop, plus the SPF, DKIM and DMARC verdicts explained in plain words and a note of anything worth a second look — a reply address on another domain, an authentication failure. Parsed in your browser, never uploaded.