ROT13 Decoder and Encoder for Spoilers and Puzzles

How to Use the ROT13 Decoder

1. Paste or type your text into the box — or press Load sample to hide the example spoiler.
2. Set the Shift amount — leave it at 13 for classic ROT13, or pick any value from 1 to 25.
3. The shifted text appears in the result box as you type or slide.
4. Copy the disguised text. To reveal it later, run it through again at the same shift (for 13) or at 26 minus your shift.

About this tool

ROT13 is the internet’s oldest spoiler tag: rotate each letter 13 places through the alphabet and text becomes unreadable at a glance, yet trivially recoverable by anyone who applies the same shift again. Forums used it for punchlines, puzzle answers and plot twists long before spoiler tags existed. Only letters move. A–Z and a–z rotate within their own case — capitals stay capital, lowercase stays lowercase — while digits, punctuation, spaces and accented characters pass through unchanged. The slider sets the distance: 13 is the preset classic, and every other value from 1 to 25 turns the tool into a general Caesar cipher, of the kind once trusted on battlefields and now used in puzzle hunts. Decoding is a matter of symmetry. At 13, simply apply the same shift again and the original returns. At any other shift n, decode by shifting 26 − n: encode at 5, decode at 21. And if you receive shifted text without being told the key, try 13 first — it is the default by tradition — then walk the slider; only 25 possibilities exist. Be clear about what this is: a disguise, not a lock. It hides text from a casual glance and teaches how classical ciphers work — and how easily they fall. The conversion runs locally in your browser, so your spoilers and puzzle drafts are never uploaded.

Worked example

Here is the sample sentence that comes with the tool, shifted by the default 13: You paste

This secret message hides plot spoilers in plain sight.

You get

Guvf frperg zrffntr uvqrf cybg fcbvyref va cynva fvtug.

Shift 13 at work: T became G and h became u, and the capital T kept its case in its new identity. The full stop did not move — punctuation never does. Paste that output back in at the same shift and the spoiler reappears, which is the whole trick of ROT13.

Features

• The full Caesar range: any shift from 1 to 25, preset to 13 for classic ROT13.
• Self-inverse at 13 — encode and decode are literally the same operation, impossible to mix up.
• Case preserved: capitals rotate within capitals, lowercase within lowercase.
• Letters only: digits, punctuation, spaces and accented characters pass through untouched.
• Instant results as you type or slide — no button, no waiting.
• Private by design: the cipher runs in your browser; your spoilers are never uploaded.