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pdfdotco

PDF.co MCP Server

Official
by pdfdotco

fill_forms

Fill existing PDF form fields with specified text values. Provide field names, page numbers, and text to populate the form programmatically.

Instructions

Fill existing form fields in a PDF document.

Example fields format:
[
    {
        "fieldName": "field_name_from_form_info",
        "pages": "1",
        "text": "Value to fill"
    }
]

Use 'read_pdf_forms_info' first to get the fieldName values of the form.

Ref: https://developer.pdf.co/api/pdf-add.md

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
urlYesURL to the source PDF file. Supports publicly accessible links including Google Drive, Dropbox, PDF.co Built-In Files Storage. Use 'upload_file' tool to upload local files.
nameNoFile name for the generated output. (Optional)
fieldsYesList of fields to fill. Each field is a dict with 'fieldName', 'pages', and 'text' properties.
api_keyNoPDF.co API key. If not provided, will use X_API_KEY environment variable. (Optional)
httppasswordNoHTTP auth password if required to access source url. (Optional)
httpusernameNoHTTP auth user name if required to access source url. (Optional)
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden. It does not disclose whether the original PDF is modified or a new file is created, nor any side effects or authentication requirements beyond what the schema implies. The example format helps but is not enough for a mutation tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is concise and front-loaded with the purpose. It includes a useful example and a prerequisite, but the reference link is optional and the structure could be slightly better organized.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, so the description should explain return values or output behavior, but it doesn't. It also doesn't mention whether this tool triggers an async job or how results are delivered, leaving significant gaps for a complex tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents all parameters. The description's example format slightly clarifies the 'fields' nested structure, but it essentially repeats schema information without adding new meaning.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states 'Fill existing form fields in a PDF document' with a specific verb and resource, distinguishing it from sibling tools like 'read_pdf_forms_info' (reading forms) and 'create_fillable_forms' (creating forms).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It provides a clear usage prerequisite: 'Use read_pdf_forms_info first to get the fieldName values'. This guides the agent on how to prepare inputs, but it doesn't explicitly compare to alternatives or state when not to use this tool.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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