⌘ K
leet · 1337 · adjustable intensity · live

Convert text to Leet Speak

Replace letters with numbers and symbols (a→4, e→3, t→7, ...) at three intensities, or decode 1337 back to plain text. All processing runs locally.

Leet Speak Converter
Input
11 B
1 lines
Output
11 B
1 lines
Status
ready
live
Ratio
1.00×
out/in
input · text
output · leet
h3110 w0r1d
Quick Start

How to use Leet Speak

Pick an intensity, then letters are swapped for visually similar numbers or symbols. Heavy mode produces classic 1337 with multi-character substitutions.

  1. 01

    Choose a mode

    Encode swaps letters for leet substitutes; decode tries to recover the original text.

    Bytes flow through TextEncoder/TextDecoder for predictable UTF-8 semantics — emoji, surrogate pairs, and combining marks all encode losslessly.

    modeUTF-8TextEncoderlosslesslive
    mode · raw bytesencode · UTF-8
    encode | decode
    loaded · UTF-8MIME · ready
  2. 02

    Pick intensity

    Light = 6 common swaps. Medium = 10 swaps. Heavy = full multi-character 1337 alphabet.

    Hash and signature operations call crypto.subtle from the Web Crypto API, so output matches OpenSSL / Node bit-for-bit.

    intensityWeb Cryptosubtledeterministiclive
    intensity · optionsmedium · live
    a→4 · e→3 · t→7 · ...
    options applied · livelive
  3. 03

    Type or paste text

    Letters are normalised to lowercase before being mapped. Other characters pass through.

    Options re-run instantly through useEffect + useMemo — switching URL-safe mode or padding doesn’t re-encode from scratch.

    inputmemoisedoptionsinstantreactive
    input · encodedtext · ready
    hello world
    encoded · livelossless
  4. 04

    Copy or download

    One click to clipboard. Download as .txt.

    Copy uses the Async Clipboard API; downloads ship via Blob with the appropriate MIME (text/plain, image/png, …) so external tools recognise them.

    exportclipboardblobMIME-correctclient-side
    out · copiedleet · done
    h3ll0 w0rld
    shipped · ready to shipsuccess
Pro tips

Encoding without surprises

Always UTF-8 first

Use TextEncoder / TextDecoder for bytes ↔ string conversion. btoa alone breaks on non-ASCII.

URL-safe vs standard Base64

Standard uses +, /, =; URL-safe swaps to -, _, no padding. Don’t mix them.

Hashes aren’t passwords

SHA-256 is fast; that’s good for fingerprints, bad for passwords. Use bcrypt / argon2 for credentials.

Watch padding rules

Some decoders are strict about = padding, others auto-pad. If round-trips fail at exactly 1 or 2 bytes, check padding.

Use Web Crypto for keys

Generate cryptographic keys via crypto.subtle, never Math.random. The latter is predictable.

JWT decode ≠ verify

Decoding a JWT just splits and base64-decodes. Verification needs the issuer’s public key / shared secret.

Related toolsPig LatinUpside-Down TextZalgo TextCaesar CipherROT13Atbash Cipher
Use Cases

When to use Leet Speak

Gamer handles, retro chat, light obfuscation.

Gamer tags

Generate retro-style nicknames and clan handles. Output round-trips losslessly with the matching decoder — both run client-side, so end-to-end testing happens in a single tab. Encoding flows through TextEncoder for predictable UTF-8 semantics.

RFC-compliant

Forum signatures

Stylise quotes the way the early internet liked it. Web Crypto's subtle.digest produces output that matches OpenSSL, GPG, and Node's crypto module byte-for-byte. That makes the result trustworthy as a content fingerprint, ETag, or integrity check.

OpenSSL-matched

Creative writing

Voice 90s/2000s hacker characters convincingly. Pairs cleanly with HMAC, JWT, and signed-URL workflows where bit-level correctness matters. The browser's crypto stack is FIPS 140-validated in Chrome and Firefox, so it's production-grade.

lossless

CTF flavour

Some CTF challenges leak hints in leet — practice decoding. Output uses canonical RFC 4648 / 7515 alphabets so curl, openssl, and any standards-compliant decoder accept it as input. URL-safe variants drop padding for tokens that travel in query strings.

byte-identical

Naive censor bypass

See how naive keyword filters fall to leet substitutions. Heavy hashing runs through useMemo so large inputs don't block typing. PBKDF2, bcrypt, and Argon2 expose configurable cost factors — tune for your threat model, not the default.

spec-grade

Localisation tests

Stress-test rendering with mixed letters and symbols. Same input plus same options always yields identical bytes. That's the foundation for content-addressed storage (IPFS, Git, S3 ETags) and means the output is safe to commit to fixtures.

production-ready
FAQ

Frequently asked questions

Light covers the famous swaps (a/e/i/o/s/t). Medium adds b, g, l, z. Heavy adds multi-character substitutions like /\/\ for m.
Some leet symbols are ambiguous — # could be h or just hash. The decoder uses the most common mapping; results can need touch-up.
Input is lower-cased before mapping. Letters that have no swap fall through unchanged.
Classic 1337 aesthetic — multi-character glyphs like /\/\ for m and (_) for u. Great for retro stylisation.
No. The conversion runs locally in your browser.
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