The A1Z26 cipher is a basic substitution cipher that swaps every letter for its position in the English alphabet. It is widely used in puzzle games, escape rooms, geocaching, and beginner cryptography lessons because it is easy to learn yet still hides plain text from a casual glance. This free tool encodes text into numbers and decodes numbers back into letters instantly, with no account and no upload.
How it works
Encoding maps each letter to a number from 1 to 26: A=1, B=2, C=3, … Z=26. The mapping is case-insensitive, so A and a both produce 1. Within a single word the numbers are joined with hyphens, and a space separates one word from the next. Any character that is not a letter — a digit, comma, or symbol — passes through unchanged.
Decoding reverses the process. Each hyphen-separated number is converted back to its letter using letter = char(96 + n), producing lowercase output. Numbers outside the 1–26 range, or items that are not whole numbers, are left exactly as typed so nothing is silently lost.
Worked example
Encode the word HELLO:
| Letter | Position |
|---|---|
| H | 8 |
| E | 5 |
| L | 12 |
| L | 12 |
| O | 15 |
Result: 8-5-12-12-15. To decode it, paste 8-5-12-12-15 and select Decode — the tool returns hello.
A complete quick-reference table for commonly used letters:
| Letter | Number | Letter | Number | Letter | Number |
|---|---|---|---|---|---|
| A | 1 | J | 10 | S | 19 |
| B | 2 | K | 11 | T | 20 |
| C | 3 | L | 12 | U | 21 |
| D | 4 | M | 13 | V | 22 |
| E | 5 | N | 14 | W | 23 |
| F | 6 | O | 15 | X | 24 |
| G | 7 | P | 16 | Y | 25 |
| H | 8 | Q | 17 | Z | 26 |
| I | 9 | R | 18 |
Where A1Z26 appears in the wild
Puzzle designers like A1Z26 because the numbers look meaningless without context but are trivially reversible once you know the scheme, making it a satisfying first layer in a multi-step cipher chain. Common sightings include escape room clue sheets, geocaching multi-caches, competitive puzzle hunts (including some UK GCHQ-style Christmas puzzles), and classroom introductions to substitution ciphers.
Limitations
A1Z26 has no key and no secret — anyone who recognises the format can decode it in seconds. Never use it to protect anything sensitive. If you need actual security, use a real cryptographic scheme. For puzzles and games, however, its simplicity is a feature: solvers feel the satisfying click of recognition when they spot a stream of numbers between 1 and 26.
Everything runs locally in your browser — your text is never sent to a server.