Felo

Alphanumeric Letter-to-Number Substitution Converter Online

Convert letters to their two-digit alphabet positions and digits to letters a–j, or decode SAC codes back to text. Ambiguous j and t codes are wrapped in colons (:010:, :020:) so results stay unambiguous, and spaces, punctuation, and unsupported characters are preserved. Try it online.

What is Alphanumeric Letter-to-Number Substitution Converter Online?

This agent performs the alphabet-position substitution cipher known as SAC. Each Latin letter becomes its two-digit place in the alphabet — A is 01, B is 02, through Z as 26 — and each digit becomes a letter, with 0 as a, 1 as b, up to 9 as j. Because the codes for j (010) and t (020) contain zeros that would blur into neighboring codes, both are wrapped in colons: j becomes :010: and t becomes :020:. The agent works in both directions, so you can paste plain text and get codes, or paste codes and get text back.

Key Features

Exact alphabet-position mapping. Every letter A–Z and a–z converts to 01–26, with lowercase letters using the same numbers as uppercase.
Colon-delimited j and t. The two ambiguous letters are always written as :010: and :020:, matching the CATS → 0301:020:019 convention.
Digit-to-letter conversion. Digits 0–9 become a–j, so 256 becomes cfg (the source page shows the same mapping in uppercase as 0B0E0F).
Two-way decoding. Paste SAC codes and the agent reconstructs the original letters and digits, including colon-delimited j and t.
Preservation reporting. Spaces, punctuation, emoji, and accented characters are kept as-is and listed so you know exactly what was not converted.

How to Use

Paste or type your text. If you want to encode, give plain English such as MEET ME AT 5, which becomes 1305 05 05 :020: 013 05 01 :020: 0f. If you want to decode, give SAC code such as 1305 05 05 :020: 013 05 01 :020: 0f, which returns MEET ME AT 5.
Say which direction you want if it is not obvious, for example “encode this” or “decode this SAC code.”
Read the converted result in the code block, then copy it. Ask for a character-by-character breakdown if you want to check each mapping.

Example Use Cases

Classroom alphabet-number exercises. Turn a spelling list into alphabet positions so students can decode it, or check a student's SAC code answer.
Puzzle and escape-room clues. Encode a short message as an alphanumeric code translator output and hand the code to players, keeping the j/t colons intact.
Verifying a mixed alphanumeric conversion. Paste something like J8T2 and confirm each character maps correctly, including the delimited j and t and the digit-to-letter step.

Tips for Best Results

Keep the colons around :010: and :020: when decoding; without them the agent cannot reliably tell a j or t code from adjacent zeros.
If your text mixes letters and digits, state the direction explicitly, since a string like 0B0E0F could be read as either input or output.
Ask for the preservation list when your text contains punctuation or non-Latin characters, so nothing is silently dropped.

FAQ

What input formats are supported?
Plain Latin text with letters, digits, spaces, and punctuation for encoding; SAC codes with two-digit groups and colon-delimited :010:/:020: for decoding. Non-Latin scripts and accented letters are preserved but not converted.

How accurate is the result?
The mapping is a fixed lookup table applied character by character, so results are deterministic. The main risk is ambiguous input direction, which the agent resolves by asking or by following your stated instruction.

How does this compare with some free text tools?
This agent states the direction rules explicitly, shows worked examples, and reports which characters were preserved rather than converted. It does not offer a random-sentence button or a live preview interface.