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About codeknife.dev

codeknife.dev is a pocketknife for code: fast developer tools in eleven languages that run in your browser. Every tool is free; membership removes the ads and raises the limits.

What it is

Encoders, formatters and testers for the small jobs developers do every day. Each tool runs on your device, is covered by automated tests, and is available in English, Dutch, German, French, Spanish, Portuguese, Turkish, Indonesian, Japanese, Chinese and Korean.

Your input stays with you

Everything runs in your browser. What you type, paste or open is never sent to our servers. The one exception is the MCP server for AI agents, which is part of the membership: what an agent you connect sends to it reaches our servers, is processed in memory and is not kept. The site is paid for by ads, which are served by third parties and load their own content, and by members, who see no ads.

  • The site sends us only a problem report, when you press Send report, an idea or vote on the idea board, a short error note when a script on the page fails, and, if you become a member, your email address for sign-in and payment. The report dialog shows exactly what will be sent.
  • The bot check for that dialog (ALTCHA) is run by us, not by a third party, and loads only when you open the dialog.
  • Tools meant for sensitive data never attach your input to a report.

Tools that chain

Every tool can send its output to the next one: decode Base64, format the JSON inside, then test a regex on the result. The hand-off happens inside your browser, never through a server.

Who makes it

Made with care in the Netherlands. codeknife.dev is an independent project. Every tool is free to use, paid for by ads or by members who choose to remove them. Articles on the blog are written by Alex Knife, a pen name of the developer behind the site. Contact: contact@codeknife.dev.

Report a problem

Found a bug or missing something? Use “Report a problem” on any tool page. You can leave an email address to hear when the fix is live.

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toolsBase64 encoder and decoderEncode text to Base64 or decode Base64 back to text, with standard and URL-safe alphabets.EncodingJSON formatter and validatorFormat, minify and validate JSON, with the exact line and column of any error.FormattingRegex testerTest JavaScript regular expressions with live highlighting, capture groups and a plain-language explanation.TextUUID and ULID generatorGenerate UUID v4, UUID v7 and ULID in bulk, or paste an ID to see its version, variant and timestamp.GeneratorsUnix timestamp converterConvert Unix timestamps to dates and back, in any time zone, with ISO 8601, RFC 2822 and relative time.Date and timeHash and HMAC generatorCalculate MD5, SHA-1, SHA-2, SHA-3, BLAKE2, BLAKE3 and CRC-32 hashes of text or a file, with optional HMAC.SecurityPassword generator and strength checkerGenerate random passwords, passphrases and PINs, or check how strong a password is.SecurityJWT decoder and verifierDecode a JSON Web Token, check its expiry and claims, and verify its signature with a secret or public key.SecurityCIDR and IP subnet calculatorCalculate the range, mask and size of IPv4 and IPv6 networks, split them into subnets, and check what contains or overlaps what.NetworkCron expression explainerRead a cron expression in plain language, see its next runs in any time zone, and tidy it into its standard form.Date and timeSort linesSort lines of text A to Z or Z to A, in natural order (file2 before file10), by code point, by number or by length.TextRemove duplicate linesRemove duplicate lines from a list, keep the first or last copy, ignore case or spaces, or drop every line that repeats.TextCompare lists and textCompare two lists line by line: find what is in both, only in one, or in either, or see a marked line diff side by side.TextText case converter and slugifyConvert text to camelCase, snake_case, kebab-case, Title Case and more, or turn a title into a URL slug with accents handled.TextURL encode, decode and parsePercent-encode and decode text for URLs, or take a URL apart into scheme, host, path and query and edit the query as a table.EncodingValidators: IBAN, BSN, VAT, card and ISBNCheck an IBAN, Dutch BSN, credit card number, EU VAT number, email address, URL or ISBN, with the reason when it fails. One value per line.ValidationHTML entity encoder and decoderEscape text for HTML with named, decimal or hex entities, or turn entities such as & and é back into characters.EncodingEscape and unescape stringsEscape text for a JSON or JavaScript string, a SQL string, a CSV field, a regular expression or a shell word, or undo the escaping.EncodingEAN, UPC and GTIN check digitsCheck the check digit of an EAN-8, EAN-13, UPC-A or GTIN-14, add a missing one, read the country from the GS1 prefix and convert between ISBN-10 and EAN-13. One code per line.ValidationTest data generatorGenerate valid-looking test IBANs, BSNs, EAN barcodes and EU VAT numbers in bulk. They pass the checks, but belong to no one.GeneratorsSQL formatter and minifierFormat SQL so each clause sits on its own line, or minify it onto one line, for MySQL, PostgreSQL, SQLite, SQL Server and BigQuery.FormattingNumber base converterConvert numbers between binary, octal, decimal, hex and any base from 2 to 36, with big numbers, two's complement and a bit view.EncodingYAML, TOML and JSON converterConvert between JSON, YAML and TOML, or validate and pretty-print a document, with the line and column of every error.FormattingCSV and JSON converterConvert CSV to a JSON array of objects or arrays, or JSON back to CSV. Detects the delimiter and reads Dutch Excel files with semicolons and decimal commas.DataGlob and .gitignore testerTest glob patterns and .gitignore rules against a list of paths and see which paths match and which rule matched them.TextColour converterConvert a colour between HEX, RGB, HSL, HWB and OKLCH, check its WCAG contrast against a background, or build a Material 3 tonal palette from it.Formattingchmod calculatorConvert Unix file permissions between octal (755), letters (rwxr-xr-x), ls -l and chmod clauses, with a checkbox grid and the setuid, setgid and sticky bits.SecurityUser-agent parserRead a user-agent string: browser, engine, OS, device type and whether it is a bot. Leave it empty to read your own browser.NetworkConvert cURL to codePaste a cURL command and get the same request as fetch, Axios, Python requests, Go or PHP. Nothing is run and nothing is sent.NetworkMarkdown previewWrite Markdown and see it rendered as you type, or copy the HTML. Raw HTML is shown as text and links are checked, so nothing in the preview can run.FormattingBarcode and QR code generatorMake a QR code, EAN-13, UPC-A, Code 128, ITF-14 or Data Matrix barcode, download it as SVG or PNG, or read a code from an image.GeneratorspagesChangelogWhat changed in each releasepagesAboutWhat codeknife.dev is and who makes itpagesIdeasSuggest improvements and vote on other visitors’ ideas.pagesPrivacyWhat leaves your browser and what is storedpagesAccessibilityConformance, known limitations and how to report a problempagesMembershipRemove ads and raise the limitspagesactions
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