Developer tools that work at the bit level.

Converters and calculators for the things underneath: bases, bits, bytes, addresses, hashes, tokens and time. Each one loads instantly and runs only in your browser.

Unsigned

48879

Signed (two's complement)

−16657

Hex

0xBEEF

Octal

0o137357

Set bits

11 of 16

As UTF-8 / ASCII

—

Click a bit. The readouts follow. Use ← → to move between bits.

Numbers & bits

Convert between bases, flip bits, and see how machines store numbers.

Base converterBinary, decimal, hex and octal, with the working shown0xBEEF = 48879 = 1011 1110 1110 1111 Bitwise calculatorAND, OR, XOR, NOT, shifts and rotates, shown bit by bit0b1100 ^ 0b1010 = 0b0110 Bitmask calculatorBuild a mask from bit positions, or decode which flags a mask containsbits 0, 2, 7 → 0x85 Two's complement converterSigned ⇄ unsigned at any width, with the invert-and-add-one steps−1 in 8 bits = 1111 1111 = 0xFF IEEE 754 float visualizerSee the sign, exponent and mantissa of any float32 or float640.1 = 0x3DCCCCCD (float32)Byte & data size converterBits, bytes, kB vs KiB, MB vs MiB, plus transfer time at a given speed1 GiB = 1.074 GB = 8,589,934,592 bits CRC & checksum calculatorCRC-8/16/32/64 in every common variant, Adler-32, Fletcher, for text or a filecrc32("123456789") = CBF43926 Endianness converterSwap byte order of 16/32/64-bit values and see the memory layout0x12345678 ⇄ 0x78563412 Gray code, BCD & popcountConvert to and from Gray code and BCD, count set bits, parity5 → Gray 111, BCD 0101 Roman numeral converterNumbers ⇄ Roman numerals, with the rules and a reference table1994 = MCMXCIV Number to wordsSpell out a number or amount in words, for cheques, contracts and invoices1,234 → one thousand two hundred and thirty-four C struct layout & bit-field visualizerPaste a struct: offsets, padding, alignment and sizeof per ABI (x86-64, ARM64, i386, ARM32, MSVC), bit-field packing, reorder to shrink, decode a hex dumpchar c; int i; → c@0, pad 3, i@4, sizeof 8 Integer overflow & arithmetic calculatorEvaluate an expression in int8…u128 with C, Rust, Go, Java or JavaScript rules: wraparound, UB, promotion, shifts, signed/unsigned trapsINT_MAX + 1 → -2147483648 (undefined behaviour in C)

Networking

Subnets, prefixes and address maths for IPv4 and IPv6.

Subnet calculatorIPv4 CIDR: network, broadcast, usable range, mask in binary, subnet splitting192.168.1.0/24 → 254 hosts IPv6 calculatorExpand or compress an address, get the prefix range, type and reverse DNS2001:db8::1/64 IP address ⇄ integerDotted IPv4 to decimal, hex, binary and octal, and back192.168.1.1 = 3232235777 MAC address lookup & formatterVendor (OUI), address type, every notation, EUI-64 and link-local address00:0C:29:… → VMware DNS lookup & mail checkerLive records from Cloudflare and Google resolvers, propagation diff, SPF include chain, DMARC and DKIMexample.com → A, MX, TXT… SPF 4 of 10 lookups Port number referenceWhat listens on which port: well-known and commonly seen TCP/UDP ports, searchable5432 → PostgreSQL DNS record explainerPaste dig output or zone lines: every record decoded, SPF, DKIM and DMARC checkedv=spf1 include:… -all → explained Packet decoderPaste tcpdump/Wireshark hex or drop a pcap: Ethernet, VLAN, ARP, IPv4/6, TCP, UDP, ICMP, DNS, DHCP, TLS decoded field by field4500 003c … → IPv4 › TCP [SYN] seq 1000 ✓ checksums CIDR aggregator & splitterMerge a list of IPs and ranges into the fewest prefixes, subtract exclusions, or split blocks10.0.0.0/25 + 10.0.0.128/25 → 10.0.0.0/24 Reverse DNS generatorPTR names, in-addr.arpa / ip6.arpa zones and bulk PTR records for a block192.168.1.0/24 → 1.168.192.in-addr.arpa User-agent parserBrowser, engine, OS, device and bot detection for any User-Agent stringMozilla/5.0 (…) Chrome/129 → Chrome 129, Windows

Encoding

Move text and bytes between the forms protocols expect.

Base64 encode / decodeStandard and URL-safe Base64 for text and files, decoded in the browserhello → aGVsbG8=URL encode / decodePercent-encoding for components, whole URLs and form data, plus a query-string parsera b&c → a%20b%26c Text ⇄ binary / hex / ASCIISee the bytes behind any text, or turn bytes back into textHi → 01001000 01101001 Hex viewerOffset, hex and ASCII columns for any file or text, like xxd in the browser00000000: 4865 6c6c 6f Hello Color converter & contrast checkerHex ⇄ RGB ⇄ HSL ⇄ OKLCH, named colors, WCAG contrast#1F4FE0 = rgb(31 79 224) = oklch(0.51 0.22 266)JSON formatter & validatorPretty-print, minify, validate with a precise error, sort keys, convert to YAML{"a":1} → pretty, YAML, stats Unicode inspectorEvery character with its code point, name, block and bytes; finds invisible and look-alike characters“pаypal” → Cyrillic а detected Text cleaner — invisible charactersStrip zero-width spaces, hidden tag characters, bidi controls, odd spaces and BOMs from text pasted from AI chats, web pages and PDFsHere’s the plan → Here’s the plan (3 hidden characters removed)Punycode / IDN converterInternationalised domain names ⇄ xn-- ASCII form, with homograph warningsmünchen.de ⇄ xn--mnchen-3ya.de HTML entity encoder / decoderNamed and numeric character references both ways, with the full HTML5 entity table© ⇄ © ⇄ ©String escape toolEscape or unescape for JSON, shell, SQL, regex, C, CSV, HTML, XML, YAML, .propertiesit's → 'it'\''s' (shell)QR code generatorURLs, Wi-Fi, contacts and text as SVG or PNG, generated in the browserhttps://… → QR (v3, M)Morse code translatorText ⇄ Morse with the full table, prosigns and audio playbackSOS = ... --- ...

Hashes & tokens

Digest, sign, decode and inspect, without sending anything anywhere.

Hash generatorMD5, SHA-1, SHA-256, SHA-384 and SHA-512 of text or a file, with HMACsha256("abc") = ba7816bf…JWT decoderRead the header and claims of a JSON Web Token, check expiry, verify HS256eyJhbGciOi… → { alg, exp, sub }UUID & ULID generatorGenerate v4, v7 and ULIDs in bulk, or inspect one to see its version and timestampv7: 019a… (sortable)Password & passphrase generatorRandom passwords and word-based passphrases with entropy in bits and time-to-crackcorrect-horse-battery-staple-river → 63 bits bcrypt, Argon2 & scrypt hasherHash a password or verify one against an existing hash, entirely in the browser$2b$12$… · $argon2id$v=19$m=19456…TOTP / 2FA code generatorPaste a Base32 secret or otpauth:// URI and get the current 6-digit code, for debugging 2FA setupsJBSWY3DPEHPK3PXP → 492039 (23 s left)SSL certificate & CSR decoderPaste a PEM certificate, CSR or public key and read every field, extension and fingerprint-----BEGIN CERTIFICATE----- → subject, SAN, expiry SSH key fingerprint & converterFingerprint an OpenSSH public key, convert OpenSSH ⇄ PEM, build authorized_keys linesssh-ed25519 AAAA… → SHA256:…HTTP security headers & CSP analyzerPaste curl -I output or a Content-Security-Policy: every header explained, graded, and the CSP evaluated for XSS bypassescurl -I → grade B · CSP: unsafe-inline, cdnjs bypass Webhook signature verifierCheck GitHub, Stripe, Slack, Shopify, Twilio, Svix and generic HMAC signatures against a payloadsha256=… matches ✓Random bytes & token generatorCryptographically random hex, Base64, API keys, numbers and dice, from your browser’s CSPRNG32 bytes → 64 hex chars

Time

Timestamps and schedules, in any time zone.

Unix timestamp converterEpoch seconds or milliseconds ⇄ dates in any time zone, with a live clock1700000000 = 2023-11-14 22:13:20 UTC Cron expression explainerPlain-English meaning of a crontab line and its next run times30 6 * * 1-5 → weekdays at 06:30 Time zone converter & meeting plannerOne moment in several zones, with a 24-hour grid to find a slot that works for everyone14:00 Belgrade = 08:00 New York = 21:00 Tokyo Date calculatorDays between two dates, business days, and add or subtract time from a date2026-01-01 → 2026-12-31 = 364 days, 261 working days Duration converterSeconds ⇄ h:m:s ⇄ ISO 8601 durations (PT1H30M), in every unit5400 s = 1 h 30 min = PT1H30M systemd timer OnCalendar explainerPlain English and next runs for OnCalendar= expressions, plus cron ⇄ systemd conversionMon..Fri *-*-* 06:30 → weekdays at 06:30

Unix

Permissions and the other bits you type into a shell.

chmod calculatorPermission checkboxes ⇄ octal ⇄ rwx, with setuid, setgid and sticky bitsrwxr-xr-x = 755 umask calculatorSee which file and directory permissions a umask produces, or find the umask for the permissions you wantumask 022 → files 644, dirs 755 ls -l and stat explainerPaste a line of ls -l or the output of stat and get every column explaineddrwxr-sr-x. 5 www-data … → directory, 2755, SELinux Exit code referenceWhat exit status 1, 2, 126, 127, 137, 139, 143 and 255 mean, and the 128+signal rule137 = killed by SIGKILL (OOM)Linux signal referenceSIGTERM vs SIGKILL, every signal number, default action and what sends itkill -15 = SIGTERM, kill -9 = SIGKILL Cron ⇄ systemd timer converterTurn a crontab line into a complete timer and service unit, or an OnCalendar expression back into cron30 6 * * 1-5 → Mon..Fri *-*-* 06:30:00 Diff toolCompare two texts line by line, see changed characters highlighted, get a unified diff- old line / + new line Regex testerLive matching with groups, replace preview, and a plain-English breakdown of the pattern/(\d{4})-(\d{2})/g → 2 groups, 3 matches nginx location testerPaste a config and a URL: which server and location win, and what rewrite, try_files and proxy_pass do with it/api/users → location /api/ → proxy http://127.0.0.1:3000/users EXPLAIN plan visualizerPaste PostgreSQL or MySQL EXPLAIN ANALYZE output: a tree with time per node, estimate vs actual, buffers, and what to fixEXPLAIN ANALYZE → 64% in Hash Join, 2 batches → raise work_mem SQL formatterPretty-print or minify SQL: PostgreSQL, MySQL, SQLite, SQL Server. Keyword case, indent, comma styleselect a,b from t where … → indented, one clause per line

Play

Puzzles and games about bits: a daily register puzzle, hex picross, and a logic-gate lab.

Bit Flip — daily register puzzleTurn the start register into the target with the fewest shifts, rotates, flips and inversions. New puzzle every day, share your result1001 1000 → 0110 1111 in 5 moves (par 5)Bit Picross — hex nonogramPaint the hidden pixel picture from the clues; every row you finish lights up as a byte. Daily 8×8 and 16×16, plus a hex-decoding racerow 3 → 0x7E · col clues 1 1 · solved!Gate Lab — build logic circuitsWire AND, OR, XOR, NOT and NAND gates to match a truth table: from an inverter to a full adder. Live simulation, 14 levelsA ⊕ B from four NANDs · full adder in 5 gates

Reference

Tables and cheat sheets to keep open in a tab or print.

HTTP status codesEvery status code with what it means and when you actually see it, including Cloudflare’s 52x502 = the proxy got nothing usable from the backend ASCII tableAll 128 ASCII codes in decimal, hex, octal and binary, with control characters, Ctrl keys, HTML and URL formsA = 65 = 0x41 = 0101 Bitwise tricks cheat sheetThe 30 bit-manipulation idioms worth knowing, with one-line explanations chmod & permissions cheat sheetOctal and symbolic chmod, special bits, umask, chown, ACLs, on one page Cron cheat sheetCrontab syntax, the 25 schedules everyone needs, environment gotchas and the commands Subnet cheat sheetIPv4 prefix table /0–/32 with masks, wildcards and host counts; private ranges; IPv6 essentials Base64 & encodings cheat sheetThe Base64, Base64URL, Base32 and hex alphabets, padding rules, sizes, and the commands in every language Regex cheat sheetMetacharacters, classes, quantifiers, groups, lookarounds, flags and the flavour differences, on one page

Why another tools site

Most converter sites are slow, covered in pop-ups, and quietly send what you paste to a server. bitlvl does the opposite: every tool is a few kilobytes of hand-written JavaScript, the page works offline once loaded, and nothing you type leaves your device. There is no account, no upload and no analytics on the content of your inputs.

Each tool also shows its working where that helps: the base converter writes out the positional expansion, the float visualizer shows the sign, exponent and mantissa, and the subnet calculator prints the mask in binary. That is the point of the name: these tools are for understanding what is going on at the bit level, not just getting a number.