FillWise MCP server

An MCP (Model Context Protocol) server that lets AI assistants such as Claude Desktop, Claude Code and Cursor fill PDF forms through the FillWise API (POST /api/v1/pdf/fill). Runs over stdio.

Tools:

• fill_pdf: takes a PDF path on disk, source text and optional attachments, writes the filled PDF next to the original (<name>.filled.pdf by default).
• fill_pdf_base64: same, but takes the PDF as base64 and returns base64. For clients without filesystem access.

Both work with AcroForm PDFs (real form fields, mode: acroform) and digital flat PDFs (no fields, values are drawn at computed positions, mode: flat). Scanned PDFs without a text layer are rejected. Review the result before using it, especially in flat mode.

Limits (set by the API): PDF up to 20 MB, data up to 60000 characters, up to 4 attachments (jpeg, png, webp or pdf, up to 5 MB each), pages as a string like "1, 3-6".

Requirements

• Node.js 18 or newer.
• A FillWise API key. Create one at https://fillwise.ai/account, section "API keys". Fills made through the API spend the account's regular fill quota.

Install and run

From npm (published, https://www.npmjs.com/package/fillwise-mcp):

npx -y fillwise-mcp

From this repository:

cd mcp && npm install
FILLWISE_API_KEY=fw_live_... node mcp/src/index.js

Environment variables:

• FILLWISE_API_KEY (required)
• FILLWISE_API_URL (optional, default https://fillwise.ai)

Claude Desktop

Add to claude_desktop_config.json (Settings, Developer, Edit Config):

{
  "mcpServers": {
    "fillwise": {
      "command": "npx",
      "args": ["-y", "fillwise-mcp"],
      "env": { "FILLWISE_API_KEY": "fw_live_..." }
    }
  }
}

Running from a local checkout instead: "command": "node", "args": ["/absolute/path/to/fillwise_app/mcp/src/index.js"].

Claude Code

claude mcp add fillwise -e FILLWISE_API_KEY=fw_live_... -- npx -y fillwise-mcp

Cursor

Add to .cursor/mcp.json in the project (or ~/.cursor/mcp.json globally):

{
  "mcpServers": {
    "fillwise": {
      "command": "npx",
      "args": ["-y", "fillwise-mcp"],
      "env": { "FILLWISE_API_KEY": "fw_live_..." }
    }
  }
}

Example prompt

"Fill /Users/me/forms/w9.pdf with the data from /Users/me/forms/company-profile.txt" or paste the details directly: "Fill /Users/me/forms/w9.pdf: JLH Associates LLC, 123 Main St, Trenton NJ 08601, EIN 12-3456789".

Errors

The tools return plain messages for the API error codes: missing or invalid key (401), scanned PDF (422), spent quota or rate limit (429), AI provider failure (502, the fill is not charged).