# JWT decoder

- Human page: https://happytails.ai/en/developer-tools/jwt-decoder/
- Markdown: https://happytails.ai/en/developer-tools/jwt-decoder.md
- Structured JSON: https://happytails.ai/agents/en/developer-tools/jwt-decoder/index.json
- Visibility: public

## Tool capabilities

| Property | Value |
| --- | --- |
| Tool ID | `jwt-decoder` |
| Category | developer-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 | /api/v1/tools/jwt-decoder/run |
| Browser-agent interface | run_current_tool |

### Implementation notes

Decoding does not verify the signature or establish trust. Tokens remain local.

### Inputs and settings

Text input: JWT.

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

```text
eyJhbGciOiJub25lIn0.eyJzdWIiOiJleGFtcGxlIn0.
```

Paste all three dot-separated sections. Decoding does not verify the signature. Results update as you type. Up to 1,000,000 characters.

No additional settings are declared for this tool.

### HTTP contract

API calls process supplied data on the server. The website origin is `https://happytails.ai`. Server API hosting is not connected on the public website yet. Use your local server origin to test these requests.

```http
POST https://happytails.ai/api/v1/tools/jwt-decoder/run
Content-Type: application/json
```

[Detailed operation reference](https://happytails.ai/en/api/tools/jwt-decoder.md) · [Shared API guide](https://happytails.ai/en/api.md)

#### Limits

| Limit | Value |
| --- | --- |
| request_bytes | 8388608 |
| input_characters | 1000000 |
| files_bytes | 5242880 |
| max_files | 0 |
| timeout_seconds | 12 |

#### Complete input schema

```json
{
  "type": "object",
  "additionalProperties": false,
  "properties": {
    "input": {
      "type": "string",
      "maxLength": 1000000,
      "default": "",
      "description": "Plain text input. File tools use files instead unless otherwise documented."
    },
    "options": {
      "type": "object",
      "additionalProperties": false,
      "properties": {}
    }
  }
}
```

#### Complete output schema

```json
{
  "type": "object",
  "required": [
    "tool",
    "result"
  ],
  "properties": {
    "tool": {
      "type": "string"
    },
    "result": {
      "type": "object",
      "required": [
        "text",
        "files"
      ],
      "properties": {
        "text": {
          "type": [
            "string",
            "null"
          ]
        },
        "data": {
          "description": "Parsed JSON when the textual result is JSON."
        },
        "name": {
          "type": "string"
        },
        "mime": {
          "type": "string"
        },
        "files": {
          "type": "array",
          "items": {
            "type": "object",
            "required": [
              "name",
              "mime",
              "bytes",
              "base64"
            ],
            "properties": {
              "name": {
                "type": "string"
              },
              "mime": {
                "type": "string"
              },
              "bytes": {
                "type": "integer"
              },
              "base64": {
                "type": "string",
                "contentEncoding": "base64"
              }
            }
          }
        }
      }
    }
  }
}
```

#### Error and retry handling

Failures return a non-200 status and `error.code` plus `error.message`. Correct invalid input before retrying; retry server-busy responses with bounded backoff. Returned files contain Base64 data, not persistent download URLs. Decode and inspect the output before treating conversion as successful. See the shared API guide for the complete status and timeout rules.

### 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

Decode header/payload locally; prominently distinguish decoding from signature verification.

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

### Complete machine-readable capability record

```json
{
  "id": "jwt-decoder",
  "category": "developer-tools",
  "built": true,
  "requirements": "Decode header/payload locally; prominently distinguish decoding from signature verification.",
  "implementation": {
    "fields": [],
    "note": "Decoding does not verify the signature or establish trust. Tokens remain local.",
    "experience": {
      "automatic": true,
      "single": true,
      "label": "JWT",
      "placeholder": "eyJhbGciOiJub25lIn0.eyJzdWIiOiJleGFtcGxlIn0.",
      "help": "Paste all three dot-separated sections. Decoding does not verify the signature. Results update as you type. Up to 1,000,000 characters.",
      "action": null
    },
    "mode": "automatic",
    "interactive": false
  },
  "execution": "POST /api/v1/tools/jwt-decoder/run",
  "api": {
    "id": "jwt-decoder",
    "name": "JWT decoder",
    "category": "developer-tools",
    "description": "Decode header/payload locally.",
    "notes": "Decoding does not verify the signature or establish trust. Tokens remain local.",
    "human_path": "/en/developer-tools/jwt-decoder/",
    "method": "POST",
    "endpoint": "/api/v1/tools/jwt-decoder/run",
    "schema_url": "/api/v1/tools/jwt-decoder",
    "input_schema": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "input": {
          "type": "string",
          "maxLength": 1000000,
          "default": "",
          "description": "Plain text input. File tools use files instead unless otherwise documented."
        },
        "options": {
          "type": "object",
          "additionalProperties": false,
          "properties": {}
        }
      }
    },
    "output_schema": {
      "type": "object",
      "required": [
        "tool",
        "result"
      ],
      "properties": {
        "tool": {
          "type": "string"
        },
        "result": {
          "type": "object",
          "required": [
            "text",
            "files"
          ],
          "properties": {
            "text": {
              "type": [
                "string",
                "null"
              ]
            },
            "data": {
              "description": "Parsed JSON when the textual result is JSON."
            },
            "name": {
              "type": "string"
            },
            "mime": {
              "type": "string"
            },
            "files": {
              "type": "array",
              "items": {
                "type": "object",
                "required": [
                  "name",
                  "mime",
                  "bytes",
                  "base64"
                ],
                "properties": {
                  "name": {
                    "type": "string"
                  },
                  "mime": {
                    "type": "string"
                  },
                  "bytes": {
                    "type": "integer"
                  },
                  "base64": {
                    "type": "string",
                    "contentEncoding": "base64"
                  }
                }
              }
            }
          }
        }
      }
    },
    "processing": "Server; same transformation code as browser tools",
    "limits": {
      "request_bytes": 8388608,
      "input_characters": 1000000,
      "files_bytes": 5242880,
      "max_files": 0,
      "timeout_seconds": 12
    }
  },
  "agent_processing": "Server; same transformation code as browser tools",
  "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

Decode header/payload locally.

## Useful next steps

- [Base64 encoder decoder](https://happytails.ai/en/developer-tools/base64-encoder-decoder/): Encode/decode tabs. ([Markdown](https://happytails.ai/en/developer-tools/base64-encoder-decoder.md))

- [Unix timestamp converter](https://happytails.ai/en/developer-tools/unix-timestamp-converter/): Seconds versus milliseconds, UTC/local zones and explicit out-of-range handling. ([Markdown](https://happytails.ai/en/developer-tools/unix-timestamp-converter.md))

- [JSON formatter](https://happytails.ai/en/developer-tools/json-formatter/): Format and validate JSON in your browser. ([Markdown](https://happytails.ai/en/developer-tools/json-formatter.md))

## How to use JWT decoder

1. Enter jwt in the input field.
2. The result updates as you type. Adjust the available settings if needed.
3. Review the result, then use Copy result or a download link when available.

## Working with jwt decoder

Formatting makes existing data or code easier to read. Validation checks whether it follows a syntax or schema. Conversion maps it into another representation. Choosing the right operation helps avoid treating a neatly formatted result as proof that the underlying data is correct.

## Common questions

### Does valid JSON mean the data is correct?

Syntax validation only establishes that the text can be parsed as JSON. A schema can check required fields and types, but neither proves that an email address, price or external record is factually correct.

### Is decoding the same as decrypting or verifying?

No. Base64 and URL encoding are representations, not encryption. Reading a token payload does not verify its signature. Use the specific validation or verification process required by the system receiving the result.

Continue your workflow: [Base64 encoder decoder](https://happytails.ai/en/developer-tools/base64-encoder-decoder/), [Unix timestamp converter](https://happytails.ai/en/developer-tools/unix-timestamp-converter/), [JSON formatter](https://happytails.ai/en/developer-tools/json-formatter/).