# Emoji Cipher Playground

> Turn secret notes into emoji and back: substitution, Caesar shift and base-emoji. Encode or decode text with three emoji ciphers: a keyed substitution (your key shuffles the emoji alphabet), a Caesar shift over an emoji alphabet, or base-emoji, which turns every UTF-8 byte into one of 256 emoji so any text survives. Round trips are exact — and the tool shows why none of this is real encryption.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://emojicipherplayground.usefulweb.site/ (interactive tool at https://emojicipherplayground.usefulweb.site/tool)
- JSON API: POST https://emojicipherplayground.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://emojicipherplayground.usefulweb.site/api/v1/tool)
- OpenAPI: https://emojicipherplayground.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://emojicipherplayground.usefulweb.site/mcp - tool `emoji_cipher_playground`

## Inputs
- action (select): Action
- scheme (select): Cipher
- text (textarea, required): Text
- key (text): Key - Substitution: shuffles the emoji alphabet. Base-emoji: optional shuffle of the byte table (empty = standard table). Not used by Caesar.
- shift (integer): Caesar shift - Letters move by this many places (mod 26), digits too (mod 10).

## Method
- Letter schemes map a–z and 0–9 to 36 emoji (🍎 a, 🐝 b, 🐱 c … and clock faces for digits). Keyed substitution shuffles that alphabet with a generator seeded by your key; Caesar shifts letters by k (mod 26) and digits by k (mod 10) before mapping.
- Capital letters get the marker 🔼 in front. Characters that would be ambiguous (the alphabet emoji themselves, 🔼, the escape emoji 🔣 and the invisible emoji variation selector) are written as 🔣 + character. Everything else (spaces, punctuation, accents) passes through unchanged. This makes decode(encode(text)) exact, which the tool verifies on every run.
- Base-emoji encodes the UTF-8 bytes of the text, one emoji per byte, using a fixed table of 256 emoji (U+1F300 upwards); an optional key shuffles the table. It works for any text, including emoji, but makes messages about 4× longer in code points.
- Security: none. Letter ciphers keep word lengths, spaces and letter frequencies (the most common emoji is probably “e”), so frequency analysis breaks them in minutes; Caesar has only 26 keys. Base-emoji is an encoding, like Base64 — with the standard table anyone can decode it. Use real encryption (e.g. age, GPG or an end-to-end encrypted messenger) for secrets.

## Limits
- A toy for puzzles, games and party invitations. It does not protect anything.