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Developer Tools

JSON, CSV, Base64, URL, XML, SQL and Markdown utilities — with exact error positions and zero uploads.

JSON Formatter & Validator{ }Format and validate JSON in your browser — pretty-print or minify with your choice of indent, and see the exact line and column when the syntax breaks.Open tool →Base64 Encoder / Decoder{ }Encode text to Base64 or decode it back — UTF-8 safe, with a URL-safe variant — using the full 64-character alphabet and padding rules printed on the page.Open tool →URL Encoder / Decoder{ }Encode a whole URL or a single query value with the right mode — component or full — and decode percent-escapes back to the text they came from, in your browser.Open tool →UUID Generator{ }Generate bulk version-4 UUIDs — one or a hundred at a time — built directly from cryptographically secure random bytes with the RFC 4122 bits set for you.Open tool →Hash Generator (SHA){ }Compute SHA-1, SHA-256, SHA-384 and SHA-512 hashes of text or a file, entirely on your device with the Web Crypto API — nothing is uploaded or stored.Open tool →Unix Timestamp Converter{ }Convert Unix timestamps to human dates and back — epoch seconds or milliseconds, UTC and your local time side by side, with a live ticking current time.Open tool →JWT Decoder{ }Decode a JSON Web Token's header and payload in your browser — claims in a table, exp and iat as real dates, expiry judged against now. Decoding only, never verification.Open tool →Regex Tester{ }Test regular expressions live — matches highlighted in your text, capture and named groups listed, flags as toggles, and a syntax cheat-sheet on the page.Open tool →Color Converter{ }Convert colours between hex, RGB, HSL and HSV with a picker and numeric fields — plus complementary, analogous, triadic and split-complementary harmonies.Open tool →Contrast Checker{ }Check text and background colour pairs against WCAG contrast rules — the exact ratio plus pass or fail for AA and AAA, normal and large text, live as you pick.Open tool →CSV to JSON Converter{ }Convert CSV to a JSON array of objects — delimiter detected automatically, quoted fields handled properly — and convert JSON back to CSV in the same tool.Open tool →HTML Entity Encoder / Decoder{ }Encode special characters as named or numeric HTML entities and decode entities back to text, with a reference table of the entities you will actually meet.Open tool →XML Formatter{ }Pretty-print XML with consistent indentation or minify it back down, with mismatched and unclosed tags reported by name instead of a silent failure.Open tool →SQL Formatter{ }Reformat tangled SQL into readable, clause-per-line queries — keywords upper or lower case, string literals left untouched — entirely in your browser.Open tool →Markdown to HTML Converter{ }Convert Markdown to clean HTML as you type, with a live preview beside the source — headings, lists, links and code rendered by GitHub-flavoured rules.Open tool →Cron Expression Generator{ }Build cron expressions by pointing and clicking, or paste one in — with a plain-words summary and the next five run times computed against your local clock.Open tool →IP Subnet Calculator{ }Work out any IPv4 subnet from an address and a prefix or netmask — network, broadcast, wildcard, usable host range and counts, with the /31 and /32 rules handled.Open tool →Number Base Converter{ }Convert integers between any bases from 2 to 36 — binary, octal, decimal, hex and beyond — with arbitrary precision, digit validation and all four common bases at once.Open tool →

About these developer tools

Developer utilities live or die on two things: whether the output is exactly right, and whether the input was safe to paste. The tools in this category are built to be exact first — the JSON formatter reports the position of a syntax error instead of merely failing, the CSV converter auto-detects whether your file is comma, semicolon, tab or pipe delimited instead of assuming commas, the Base64 tool is UTF-8 safe rather than assuming Latin-1, and the URL encoder makes you choose between component and full-URL mode because confusing the two is how query strings get double-encoded. The SQL and XML formatters don't just indent: the XML tool validates tag nesting and names the mismatched tag, and the SQL tool puts each clause on its own line while leaving string literals and dotted identifiers untouched.

The second requirement is privacy, and for developers it is not abstract. The things pasted into formatters and decoders during a working day are production payloads, config files, tokens, customer rows and log excerpts — exactly the data that should never be sent to a stranger's server to have its brackets matched. Every tool here runs entirely in your browser: the JSON you validate, the CSV you convert and the Markdown you preview are processed on your device and are never uploaded, stored or logged. That is also why the category is honest about limits — decoding shows you what a payload contains and never claims to verify it, and the Base64 tool handles files locally rather than asking you to upload them anywhere.

The workflow pattern repeats across the category: paste on the left, get formatted, converted or validated output on the right, copy or download it, and move on. Where a pair of tools are inverses — CSV to JSON and JSON to CSV live in one tool with a direction switch, as do the Base64 and URL encoder/decoders — they share a page rather than forcing you to find the reverse tool. New utilities join this category only when they can meet the same bar: deterministic output, errors explained in words, and nothing leaving the machine.

Frequently asked questions

Is it safe to paste production JSON or CSV data into these tools?

The processing is safe by construction: every developer tool on Kwikfig runs 100% in your browser, so your payload never travels over the network, is never stored and is never logged. You can verify this by loading a tool, disconnecting from the network, and using it — it works identically offline.

Why does the JSON tool show an error position instead of fixing my JSON?

Because silently 'repairing' JSON means guessing what you meant — dropping a trailing comma is harmless, but guessing at a missing quote or bracket can change your data's meaning. The formatter validates strictly and tells you where the first problem is (with line and column when the parser reports a position), so the fix is yours and deliberate.

What is the difference between URL component and full-URL encoding?

Component mode (encodeURIComponent) escapes everything that has structural meaning in a URL — slashes, question marks, ampersands, equals signs — so a value can be safely embedded inside a query string. Full-URL mode (encodeURI) leaves that structure intact and only escapes characters that cannot appear in a URL at all, like spaces. The URL Encoder page explains which mode each job needs; using the wrong one is the classic cause of double-encoded or broken links.