# Caesar cipher encoder and decoder

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

## Tool capabilities

| Property | Value |
| --- | --- |
| Tool ID | `caesar-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

Shifts A–Z while preserving case, spaces and punctuation. Shift 13 is ROT13. This historical cipher is easily broken and must not be used to protect secrets.

### 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 |
| --- | --- | --- | --- | --- |
| `shift` | Shift (use a negative value to decode) | number | 13 | min=-25 max=25 step=1 |

### 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

Shifts A–Z while preserving case, spaces and punctuation. Shift 13 is ROT13. This historical cipher is easily broken and must not be used to protect secrets.

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

### Complete machine-readable capability record

```json
{
  "id": "caesar-cipher",
  "category": "text-tools",
  "built": true,
  "requirements": "Shifts A–Z while preserving case, spaces and punctuation. Shift 13 is ROT13. This historical cipher is easily broken and must not be used to protect secrets.",
  "implementation": {
    "fields": [
      {
        "key": "shift",
        "label": "Shift (use a negative value to decode)",
        "value": 13,
        "type": "number",
        "min": -25,
        "max": 25,
        "step": 1
      }
    ],
    "live": true,
    "note": "Shifts A–Z while preserving case, spaces and punctuation. Shift 13 is ROT13. This historical cipher is easily broken and must not be used to protect secrets.",
    "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

Shift letters to create or solve a simple cipher puzzle.

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 Caesar cipher encoder and decoder

1. Enter text and choose a shift from -25 to 25. Use the opposite shift to decode. A shift of 13 is ROT13 and applying it twice restores the original.
2. With shift 13, Hello, World! becomes Uryyb, Jbeyq!. Punctuation and capitalization are preserved.

## Useful next steps

- [Vigenère cipher encoder and decoder](https://happytails.ai/en/text-tools/vigenere-cipher/) ([Markdown](https://happytails.ai/en/text-tools/vigenere-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))

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

## How to use it

Enter text and choose a shift from -25 to 25. Use the opposite shift to decode. A shift of 13 is ROT13 and applying it twice restores the original.

### Try a small example

With shift 13, Hello, World! becomes Uryyb, Jbeyq!. Punctuation and capitalization are preserved.

### What to know

Shifts A–Z while preserving case, spaces and punctuation. Shift 13 is ROT13. This historical cipher is easily broken and must not be used to protect secrets.