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AssemblyJustin

Assembly MCP

Assembly MCP

A small Model Context Protocol server that gives any MCP client (Claude Code, Claude Desktop, …) two document-conversion tools:

Tool

Direction

Engine

convert_pdftomd

PDF → Markdown

PyMuPDF

convert_mdtopdf

Markdown → PDF

WeasyPrint

Both are the conversion engines Assembly already standardises on: PyMuPDF-first extraction (font-size heading detection, running header/footer removal, table extraction, watermark stripping) and WeasyPrint for Markdown/HTML → PDF (pure-Python, no TeX toolchain).


Requirements

  • Python ≥ 3.11

  • uv (recommended) or pip

  • WeasyPrint native libraries — only needed for convert_mdtopdf (convert_pdftomd works without them):

    • Linux (Debian/Ubuntu): apt install libpango-1.0-0 libpangoft2-1.0-0 libgdk-pixbuf-2.0-0 libffi-dev

    • macOS: brew install pango gdk-pixbuf libffi

    • Windows: install the GTK3 runtime. Without it, convert_pdftomd still works and convert_mdtopdf returns a clear "install GTK" error.


Related MCP server: mcp-pdf2md

Install

git clone https://github.com/AssemblyJustin/assembly-mcp.git
cd assembly-mcp
uv sync            # creates .venv and installs everything

Run the server directly to confirm it starts (it speaks MCP over stdio and will wait for a client — Ctrl-C to exit):

uv run assembly-mcp

Add to Claude Code

From anywhere, register the server (adjust the path to your clone):

claude mcp add assembly -- uv --directory /ABSOLUTE/PATH/TO/assembly-mcp run assembly-mcp

Then the tools convert_pdftomd and convert_mdtopdf are available in your session. This repo also ships matching slash commands — run Claude Code from inside the repo (or copy .claude/commands/* into your project) to use:

/convert-pdftomd  report.pdf  report.md
/convert-mdtopdf  notes.md     notes.pdf

Add to Claude Desktop

Edit claude_desktop_config.json (macOS: ~/Library/Application Support/Claude/, Windows: %APPDATA%\Claude\) and add:

{
  "mcpServers": {
    "assembly": {
      "command": "uv",
      "args": ["--directory", "C:\\ABSOLUTE\\PATH\\TO\\assembly-mcp", "run", "assembly-mcp"]
    }
  }
}

Restart Claude Desktop. The two tools appear under the 🔌 tools menu.


Tools

convert_pdftomd

Convert a PDF file to Markdown.

Argument

Type

Default

Description

pdf_path

string

Path to the source .pdf.

output_path

string

null

Optional path to also write the .md.

strip_watermarks

bool

true

Remove Standards-NZ / IHS style watermark lines and light-grey overlay text.

front_matter

bool

true

Prepend YAML front-matter linking back to the source PDF.

Returns the Markdown text. Extraction features: font-size heading map (largest sizes → #..####), running header/footer removal, find_tables() → pipe tables, watermark/licence-line stripping.

This is a code-only extraction (Tiers 1–2 of Assembly's pipeline). It does not run the vision-based Tier 3–4 verification, so treat the output as a high-quality first pass, not a certified copy.

convert_mdtopdf

Convert Markdown to a PDF file. Provide either md_path or markdown_text.

Argument

Type

Default

Description

output_path

string

Where to write the .pdf (required).

md_path

string

null

Path to a source .md.

markdown_text

string

null

Raw Markdown (alternative to md_path).

title

string

null

Document title (falls back to front-matter title).

css

string

null

CSS to replace the built-in print stylesheet.

Renders Markdown → HTML → PDF with a clean A4 print stylesheet (tables, code blocks, page numbers) and verifies the PDF magic bytes before writing.


Develop

uv run pytest            # smoke tests (MD→PDF test auto-skips without GTK)

Project layout:

src/assembly_mcp/
  server.py       FastMCP server — registers both tools (stdio)
  pdf_to_md.py    PyMuPDF extraction pipeline
  md_to_pdf.py    python-markdown → WeasyPrint rendering
.claude/commands/ /convert-pdftomd and /convert-mdtopdf slash commands
tests/            round-trip smoke test

License

MIT — see LICENSE.

Available Tools

2 tools
convert_mdtopdfA

Convert Markdown to a PDF file.

Renders Markdown → HTML → PDF with WeasyPrint (the Assembly MD→PDF stack)
using a clean print stylesheet. Provide EITHER `md_path` OR `markdown_text`.
A PDF is binary, so `output_path` is required.

Args:
    output_path: Path to write the resulting `.pdf` (required).
    md_path: Path to a source `.md` file.
    markdown_text: Raw Markdown string (alternative to `md_path`).
    title: Optional document title (falls back to front-matter `title`).
    css: Optional CSS to replace the built-in print stylesheet.

Returns:
    A confirmation string with the output path, byte size, and page count.
ParametersJSON Schema
NameRequiredDescriptionDefault
cssNo
titleNo
md_pathNo
output_pathYes
markdown_textNo

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A4.4/5.0
Behavior4/5

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

With no annotations provided, the description fully carries the burden of behavioral disclosure. It reveals the rendering stack (WeasyPrint), input alternatives, the binary nature of output requiring a path, the title fallback to front-matter, and the exact return format (confirmation string with output path, byte size, page count). It does not mention overwrite behavior or error conditions when both inputs are provided, but the disclosed details substantially exceed what a minimal description would provide.

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 longer than average but well-structured: a one-line purpose, a pipeline/usage explanation, an Args list, and a Returns note. Every sentence carries information—there is no filler or repetition of schema fields. The front-loaded purpose sentence ensures the core meaning is immediately visible.

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

Completeness4/5

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

Given the tool has 5 parameters, 0% schema description coverage, no annotations, and an output schema, the description covers the essentials well: pipeline, input constraints, parameter semantics, and return value format. Minor gaps exist—such as overwrite policy or behavior when both md_path and markdown_text are supplied—but the description is largely complete for an AI agent to select and use the tool correctly.

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

Parameters5/5

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

Schema description coverage is 0%, so the description must compensate entirely. It does so comprehensively with an Args block that explains all five parameters: output_path (required), md_path, markdown_text (the alternative), title (with fallback behavior), and css (replacement for built-in stylesheet). This adds meaning far beyond the bare schema types and defaults.

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 opens with a specific verb+resource: 'Convert Markdown to a PDF file.' It then details the rendering pipeline (Markdown → HTML → PDF with WeasyPrint), which clearly distinguishes this tool from its sibling convert_pdftomd (the reverse conversion). This is a precise, unambiguous purpose statement.

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?

The description provides clear usage context: 'Provide EITHER `md_path` OR `markdown_text`' and explains why `output_path` is required (PDF is binary). It also notes the title fallback behavior and CSS replacement option. However, it does not explicitly name convert_pdftomd as the alternative for the reverse conversion, so it stops short of an explicit when-not-to-use statement.

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

convert_pdftomdA

Convert a PDF file to Markdown.

Uses PyMuPDF with font-size heading detection, running header/footer
removal, table extraction, and optional watermark stripping — the Assembly
PDF→MD pipeline. Returns the Markdown text; when `output_path` is given it
also writes a `.md` file there.

Args:
    pdf_path: Path to the source `.pdf` file.
    output_path: Optional path to also write the Markdown to (`.md`).
    strip_watermarks: Remove Standards-NZ / IHS style watermark lines and
        light-grey overlay text.
    front_matter: Prepend YAML front-matter linking back to the source PDF.

Returns:
    The converted Markdown as a string.
ParametersJSON Schema
NameRequiredDescriptionDefault
pdf_pathYes
output_pathNo
front_matterNo
strip_watermarksNo

Output Schema

ParametersJSON Schema
NameRequiredDescription
resultYes

TDQS

A4.6/5.0
Behavior5/5

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

With no annotations, the description fully discloses the conversion process (PyMuPDF, heading detection, header/footer removal, table extraction), optional watermark stripping, side effects (writing a file when output_path is given), and the return value. This goes well beyond basic expectations.

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

Conciseness5/5

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

The description is well-structured with a clear summary, Args section, and Returns section. It is appropriately sized for a tool with four parameters, and every sentence adds value without redundancy.

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

Completeness5/5

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

The description is complete: it covers the conversion process, all parameters, side effects, and return value. The presence of an output schema doesn't override the need for context, and the description provides rich behavioral context.

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

Parameters5/5

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

Schema description coverage is 0%, so the description must explain each parameter. It does so clearly: pdf_path as source .pdf, output_path as optional write target, strip_watermarks for specific watermark removal, and front_matter for YAML prepending. This adds meaning beyond the raw schema.

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 the tool's function: 'Convert a PDF file to Markdown.' It identifies the specific resource (PDF), the output format (Markdown), and the direction of conversion, which distinguishes it from the sibling tool convert_mdtopdf.

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

Usage Guidelines3/5

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

The description implies usage by stating the conversion direction and pipeline details, but it does not explicitly mention when to use this tool instead of the sibling convert_mdtopdf, nor does it provide any exclusions or alternative scenarios.

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

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections.

  1. 2 tool updatesv0.1.0
    • First observedconvert_mdtopdf
    • First observedconvert_pdftomd

TDQS

A4.6/5.0

Scored across 2 tools

Disambiguation5/5

The two tools are exact inverses: one converts PDF to Markdown, the other Markdown to PDF. There is zero overlap or ambiguity between them.

Naming Consistency5/5

Both tool names follow the identical convert_<source>to<target> pattern (convert_pdftomd, convert_mdtopdf). The naming is perfectly consistent and predictable.

Tool Count4/5

The server has only 2 tools, which is on the low end, but the scope is tightly focused on bidirectional PDF/Markdown conversion. The count is slightly under the typical 3-15 range yet entirely reasonable for the stated purpose.

Completeness5/5

The tool surface fully covers the domain of PDF-Markdown conversion in both directions. There are no obvious missing operations for a conversion-focused utility.

Maintenance

ActivityStale
ResponsivenessNo issues

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