# Vigenère cipher encoder and decoder

- Human page: https://happytails.ai/en/text-tools/vigenere-cipher/
- Markdown: https://happytails.ai/en/text-tools/vigenere-cipher.md
- Structured JSON: https://happytails.ai/agents/en/text-tools/vigenere-cipher/index.json
- Visibility: public

## Tool capabilities

| Property | Value |
| --- | --- |
| Tool ID | `vigenere-cipher` |
| Category | text-tools |
| Implementation | Registered implementation. Registration alone is not a production-quality guarantee. |
| Browser execution | Automatic updates after valid input or file selection. |
| Browser processing | Browser; see tool notes for network behavior. |
| HTTP API | Not callable through HTTP. |
| Browser-agent interface | run_current_tool |

### Implementation notes

Repeats a letter key over A–Z; spaces and punctuation do not advance the key. For puzzles and learning only. It is not secure encryption.

### Inputs and settings

Text input: Your text.

Example or placeholder shown in the interface (not a validated fixture):

```text
Type or paste your input…
```

Change the input or settings to update your result. Results update as you type. Up to 1,000,000 characters.

| Setting | Meaning | Control type | Default | Constraints |
| --- | --- | --- | --- | --- |
| `key` | Key (letters A–Z) | text | "LEMON" |  |
| `direction` | Direction | select | "Encode" | Allowed: Encode, Decode |

### Browser-agent workflow

1. Open the human page in a browser that supports WebMCP.
2. Discover the interface exposed by that page; use its actual schema.
3. Select files on the page first when the tool requires files.
4. Call `run_current_tool` with valid input and settings.
5. Inspect the returned result or error and the displayed output. Retrieve files from the displayed download links.

Calls do not automatically copy or download results. Browser permissions still apply. Interface availability alone is not proof of successful execution.

### Planning specification

Repeats a letter key over A–Z; spaces and punctuation do not advance the key. For puzzles and learning only. It is not secure encryption.

This describes intended requirements. Use the implementation notes, interface schema and observed output to determine current support.

### Complete machine-readable capability record

```json
{
  "id": "vigenere-cipher",
  "category": "text-tools",
  "built": true,
  "requirements": "Repeats a letter key over A–Z; spaces and punctuation do not advance the key. For puzzles and learning only. It is not secure encryption.",
  "implementation": {
    "fields": [
      {
        "key": "key",
        "label": "Key (letters A–Z)",
        "value": "LEMON",
        "type": "text"
      },
      {
        "key": "direction",
        "label": "Direction",
        "value": "Encode",
        "type": "select",
        "values": [
          "Encode",
          "Decode"
        ]
      }
    ],
    "live": true,
    "note": "Repeats a letter key over A–Z; spaces and punctuation do not advance the key. For puzzles and learning only. It is not secure encryption.",
    "experience": {
      "automatic": true,
      "single": false,
      "inputMaxLength": 1000000,
      "inputMode": "text",
      "label": "Your text",
      "placeholder": "Type or paste your input…",
      "help": "Change the input or settings to update your result. Results update as you type. Up to 1,000,000 characters.",
      "action": null
    },
    "mode": "automatic",
    "interactive": false
  },
  "execution": "Browser interface",
  "api": null,
  "browser_agent": {
    "supported": true,
    "name": "run_current_tool",
    "discovery": "WebMCP on the human page in a supporting browser",
    "verification": "See audit/API-AUDIT.md; availability is not verification"
  }
}
```

## Page guide

Make a repeating-key letter cipher for a puzzle or lesson.

How can we improve this tool?

Report a problem or share an idea.

Please leave out private information. Your message and the tool name go to our team via PostHog.

### How to use Vigenère cipher encoder and decoder

1. Enter your message, a key containing letters A–Z, and choose Encode or Decode. The key repeats across letters only; spaces and punctuation do not consume a key character.
2. ATTACK AT DAWN with key LEMON becomes LXFOPV EF RNHR. Choose Decode with the same key to restore it.

## Useful next steps

- [Caesar cipher encoder and decoder](https://happytails.ai/en/text-tools/caesar-cipher/) ([Markdown](https://happytails.ai/en/text-tools/caesar-cipher.md))

- [Morse code translator](https://happytails.ai/en/text-tools/morse-code-translator/) ([Markdown](https://happytails.ai/en/text-tools/morse-code-translator.md))

- [Uppercase](https://happytails.ai/en/text-tools/uppercase/) ([Markdown](https://happytails.ai/en/text-tools/uppercase.md))

## How to use it

Enter your message, a key containing letters A–Z, and choose Encode or Decode. The key repeats across letters only; spaces and punctuation do not consume a key character.

### Try a small example

ATTACK AT DAWN with key LEMON becomes LXFOPV EF RNHR. Choose Decode with the same key to restore it.

### What to know

Repeats a letter key over A–Z; spaces and punctuation do not advance the key. For puzzles and learning only. It is not secure encryption.