Is ROT13 secure encryption?

No. ROT13 is a Caesar cipher with a fixed shift of 13 — it provides no cryptographic security. It is used for obscuring spoilers, puzzles, and joke punchlines, not for protecting data.

Why is the same operation used to encode and decode?

There are 26 letters in the English alphabet and ROT13 shifts by 13. Applying the shift twice (13 + 13 = 26) returns the original letter, so encoding and decoding are the same function.

What happens to numbers, punctuation, and other characters?

Only the 26 ASCII letters A–Z and a–z are rotated. Digits, punctuation, whitespace, and non-Latin characters pass through unchanged.

Is my text sent to a server?

No. The rotation is a few lines of JavaScript that run locally in your browser. Nothing is uploaded or logged.

rot13 · self-inverse · letters only · live

Encode and decode ROT13

Shift each letter 13 places — the classic spoiler-hiding cipher. Encoding and decoding are the same operation. Runs locally in your browser.

ROT13 Converter

Input

39 B

1 lines

Output

39 B

1 lines

Status

ready

live

Ratio

1.00×

out/in

input · text

output · rot13

Uryyb, Jbeyq! EBG13 vf vgf bja vairefr.

Quick Start

How to use ROT13

ROT13 shifts every letter by 13 positions. Because 13+13=26, applying it twice returns the original — a quirk that makes it self-inverse.

01
Type or paste text
Any letters work; digits and punctuation pass through unchanged.
Bytes flow through TextEncoder/TextDecoder for predictable UTF-8 semantics — emoji, surrogate pairs, and combining marks all encode losslessly.
inputUTF-8TextEncoderlosslesslive
input · raw bytestext · UTF-8
```
Hello, World!
```
loaded · UTF-8MIME · ready
02
Shift by 13
A → N, B → O, ..., N → A. Case is preserved.
Hash and signature operations call crypto.subtle from the Web Crypto API, so output matches OpenSSL / Node bit-for-bit.
shiftWeb Cryptosubtledeterministiclive
shift · options+13 · live
```
A→N · B→O · ...
```
options applied · livelive
03
Live preview
Result updates as you type. Same button decodes — ROT13 is symmetric.
Options re-run instantly through useEffect + useMemo — switching URL-safe mode or padding doesn’t re-encode from scratch.
livememoisedoptionsinstantreactive
out · encodedrot13 · ready
```
Uryyb, Jbeyq!
```
encoded · livelossless
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
ok · copiedready · done
```
Copied
```
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.

Use Cases

When to use ROT13

Spoilers, mild obfuscation, puzzle hints.

Hide spoilers

Forum posts and reviews where readers can opt-in to decode. 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

Puzzles & CTFs

Beginner crypto challenges almost always feature ROT13. 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

Email signatures

Light obfuscation for inline jokes or trivia answers. 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

Learning crypto

Simplest example of a substitution cipher. 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

Old Usenet posts

Decode archives that used ROT13 by convention. 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

Browser plugins

Verify what a ROT13 extension would produce. 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

Why does ROT13 not need a decode button?

Because 13 + 13 = 26, the same shift restores the original text. Run the encoder twice and you get the input back.

Does it handle non-Latin letters?

No — only A-Z and a-z are shifted. Digits, punctuation, and Unicode pass through untouched.

Is it secure?

Not at all. ROT13 is a fixed-shift cipher with no key. Use it only to hide spoilers, never to protect anything sensitive.

Whats the difference from Caesar?

ROT13 is the Caesar cipher with shift=13. The Caesar Cipher tool exposes any shift from 1 to 25.

Is anything sent to a server?

No. Encoding runs locally in your browser.

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