pdfcraft/crates/automation/README.md

pdfcraft-automation

Agent control for PdfCraft: a headless tool table over the engine, and an opt-in MCP server.

• Layer: L7 (architecture §13), but headless. It depends on engine, render and organize, never on a UI toolkit.
• Status: over a hundred tools; pdfcraft-cli tools lists the current set with their schemas (the count isn't repeated here, so it can't go stale). They cover inspection, rendering, text, page edits and organizing, page labels, bookmarks, comments and their review, form filling and authoring (fields, properties, scripts, data exchange, detection), redaction and sanitizing, password protection and signatures, adding text, images, links and stamps, optimizing, OCR, printing, export, metadata, undo/redo, save, combine, extract and split. Comment tools take geometry in the same top-left-origin points as everything else, and comment_add can mark text by searching for it (find). The MCP server also serves the open documents as resources, page images included. The running app's UI is driven separately, through the ui.* control channel in pdfcraft-ui-egui.

API

let mut a = Automation::new().with_root("/work")?;      // optional: confine all paths
let doc = a.call("doc_open", &json!({ "path": "in.pdf" }))?;   // Vec<Content>
tools() -> Vec<ToolDef>                                  // name, title, description, input_schema, read_only, destructive, command
mcp::McpServer::new(a).serve(stdin, stdout)?             // newline-delimited JSON-RPC 2.0

Content is Json(Value) or Png { data, width, height }. Errors are UnknownTool, InvalidArgs (the call didn't match the schema) or Failed (a readable message for the agent).

Conventions

• Tool names are snake_case (page_rotate): MCP clients reject dots. ToolDef::command links a tool to the registry id it automates (page.rotate), and command_list reports the link.
• Pages and positions are 1-based. Rectangles are PDF points with the origin at the top-left of the displayed page.
• Unknown arguments are rejected, so typos fail loudly.
• Tools that change a document return its summary (doc, pages, dirty, undo, redo, …).
• doc_close refuses to drop unsaved changes unless discard_changes: true. doc_save writes atomically, incrementally in place, and in full for a new path.
• With a root set, every read and write path must resolve inside it (symlinks and .. included).

MCP server

Opt-in only. Nothing starts it automatically, and it opens no port. It runs while pdfcraft-cli mcp [--root DIR] runs, normally launched by an agent from its MCP configuration. It stops when stdin closes. The CLI's mcp Cargo feature (on by default) compiles it out entirely when disabled.

Implemented: initialize (protocol 2025-06-18, 2025-03-26, 2024-11-05), ping, tools/list (with readOnlyHint/destructiveHint annotations), tools/call (JSON results also returned as structuredContent; images as image/png), and resources/list, resources/templates/list and resources/read. The resources expose the open documents read-only: pdfcraft://doc/{doc}/info (JSON), …/text, …/page/{page}/text and …/page/{page}/image{?dpi} (PNG, 1–600 dpi). Tool failures come back as isError: true results, so the agent can read and recover from them.

Adding a tool

1. Add the engine capability first, with its tests (the tool is a thin adapter).
2. Add a ToolDef in src/tools.rs: a precise description, the schema, ro()/destructive(), and cmd() if a registry command exists.
3. Handle it in Automation::call, validating pages and positions with the existing helpers.
4. Add an end-to-end test in tests/automation.rs. tool_table_is_well_formed checks names, schemas and command links.