# Fill PDF

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

## Tool capabilities

| Property | Value |
| --- | --- |
| Tool ID | `fill-pdf` |
| Category | pdf-tools |
| Implementation | Registered implementation. Registration alone is not a production-quality guarantee. |
| Browser execution | Use the visible action or interactive controls. |
| Browser processing | Browser; see tool notes for network behavior. |
| HTTP API | /api/v1/tools/fill-pdf/run |
| Browser-agent interface | run_current_tool |

### Implementation notes

Run with blank input to list field names. Then enter a JSON object mapping field names to values. Supports text, checkbox and choice fields.

### Inputs and settings

Text input: Your text.

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

```text
Type or paste your input…
```

Up to 1,000,000 characters. Review the settings before running.

Accepted browser files: `.pdf`. Choose one file.

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/fill-pdf/run
Content-Type: application/json
```

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

#### Limits

| Limit | Value |
| --- | --- |
| request_bytes | 8388608 |
| input_characters | 1000000 |
| files_bytes | 5242880 |
| max_files | 1 |
| 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": {}
    },
    "files": {
      "type": "array",
      "maxItems": 1,
      "items": {
        "type": "object",
        "required": [
          "name",
          "base64"
        ],
        "additionalProperties": false,
        "properties": {
          "name": {
            "type": "string",
            "maxLength": 200,
            "description": "Filename only, no path."
          },
          "mime": {
            "type": "string",
            "maxLength": 150
          },
          "bytes": {
            "type": "integer",
            "minimum": 0,
            "description": "Optional decoded byte count; must match content if supplied."
          },
          "base64": {
            "type": "string",
            "contentEncoding": "base64",
            "description": "File bytes as padded base64. Use the tool-specific limits.files_bytes value for the total decoded input size."
          }
        }
      }
    }
  }
}
```

#### 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

Fill supported AcroForms; detect unsupported XFA; test field appearance.

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

### Complete machine-readable capability record

```json
{
  "id": "fill-pdf",
  "category": "pdf-tools",
  "built": true,
  "requirements": "Fill supported AcroForms; detect unsupported XFA; test field appearance.",
  "implementation": {
    "fields": [],
    "files": true,
    "accept": ".pdf",
    "note": "Run with blank input to list field names. Then enter a JSON object mapping field names to values. Supports text, checkbox and choice fields.",
    "experience": {
      "automatic": false,
      "single": false,
      "label": "Your text",
      "placeholder": "Type or paste your input…",
      "help": "Up to 1,000,000 characters. Review the settings before running.",
      "action": null
    },
    "mode": "explicit",
    "interactive": false
  },
  "execution": "POST /api/v1/tools/fill-pdf/run",
  "api": {
    "id": "fill-pdf",
    "name": "Fill PDF",
    "category": "pdf-tools",
    "description": "Fill existing PDF form fields with values you provide.",
    "notes": "Run with blank input to list field names. Then enter a JSON object mapping field names to values. Supports text, checkbox and choice fields.",
    "human_path": "/en/pdf-tools/fill-pdf/",
    "method": "POST",
    "endpoint": "/api/v1/tools/fill-pdf/run",
    "schema_url": "/api/v1/tools/fill-pdf",
    "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": {}
        },
        "files": {
          "type": "array",
          "maxItems": 1,
          "items": {
            "type": "object",
            "required": [
              "name",
              "base64"
            ],
            "additionalProperties": false,
            "properties": {
              "name": {
                "type": "string",
                "maxLength": 200,
                "description": "Filename only, no path."
              },
              "mime": {
                "type": "string",
                "maxLength": 150
              },
              "bytes": {
                "type": "integer",
                "minimum": 0,
                "description": "Optional decoded byte count; must match content if supplied."
              },
              "base64": {
                "type": "string",
                "contentEncoding": "base64",
                "description": "File bytes as padded base64. Use the tool-specific limits.files_bytes value for the total decoded input size."
              }
            }
          }
        }
      }
    },
    "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": 1,
      "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

Fill existing PDF form fields with values you provide.

## Useful next steps

- [Merge PDF](https://happytails.ai/en/pdf-tools/merge-pdf/): Combine PDF files into one document. ([Markdown](https://happytails.ai/en/pdf-tools/merge-pdf.md))

- [Split PDF](https://happytails.ai/en/pdf-tools/split-pdf/): Save selected PDF pages as separate files. ([Markdown](https://happytails.ai/en/pdf-tools/split-pdf.md))

- [Extract pages](https://happytails.ai/en/pdf-tools/extract-pages/): Create a PDF containing the pages you select. ([Markdown](https://happytails.ai/en/pdf-tools/extract-pages.md))

## How to use Fill PDF

1. Choose a file in PDF.
2. Review the settings, then choose Run Fill PDF.
3. Review the result, then use Copy result or a download link when available.

## What to expect

Fill existing PDF form fields with values you provide. Choose a PDF and run with blank input to list its field names. Then enter a JSON object mapping those names to values and run again to download the filled PDF.