Dependencies for Exporting PNG Diagrams with diagram-design: Playwright Setup Guide

Exporting diagrams to PNG in diagram-design requires only one external runtime dependency: the Playwright Python library paired with a Chromium browser binary.

The cathrynlavery/diagram-design repository handles PNG rasterization through a streamlined workflow that leverages headless browser automation. Understanding these dependencies ensures you can generate high-quality diagram exports without unnecessary package bloat.

Core PNG Export Dependencies

Playwright and Chromium Requirements

The PNG export functionality relies exclusively on Playwright as its runtime engine. Unlike traditional diagram libraries that require complex native graphics libraries, diagram-design uses Playwright to launch a Chromium browser instance, render the generated HTML, and capture a screenshot of the <svg> element.

According to the source code in skills/diagram-design/references/export.md (lines 55-68), the system explicitly checks for Playwright availability before proceeding with any export operation. If the library is not detected, the workflow halts and prompts the user to complete the installation. This design choice eliminates the need for additional third-party graphics packages or system-level dependencies beyond the browser binary itself.

Installation Steps

Setting up the PNG export capability requires a one-time installation of Playwright and its corresponding Chromium binary. As documented in the repository's README.md (lines 9-11), you must execute the following commands:

# Install the Python Playwright library

pip install playwright

# Download the Chromium browser binary (one-time setup)

playwright install chromium

These commands establish the complete runtime environment necessary for PNG generation. The playwright install chromium step downloads a compatible browser version managed by Playwright, ensuring consistent rendering across different operating systems without relying on system-installed browsers.

How PNG Export Works Internally

The internal implementation detailed in skills/diagram-design/references/export.md demonstrates how the library orchestrates the screenshot capture. Playwright launches Chromium, loads the diagram HTML file via a local file protocol, waits for the network to idle, and targets the first <svg> element for capture:

from playwright.sync_api import sync_playwright
import sys, pathlib

src, out = sys.argv[1], sys.argv[2]
scale = int(sys.argv[3]) if len(sys.argv) > 3 else 2

with sync_playwright() as p:
    browser = p.chromium.launch()
    page = browser.new_page(device_scale_factor=scale)
    page.goto(f"file://{pathlib.Path(src).resolve()}")
    page.wait_for_load_state("networkidle")
    page.locator("svg").first.screenshot(path=out, omit_background=True)
    browser.close()

The device_scale_factor parameter controls the resolution of the output PNG, defaulting to a scale factor of 2 for high-DPI clarity. The omit_background=True setting ensures transparent backgrounds when the SVG does not specify a solid fill.

Command-Line Usage

Once dependencies are installed, you can trigger PNG exports using the CLI interface defined in commands/export-diagram.md. The --png-only flag restricts output to PNG format, while the --scale parameter adjusts the resolution multiplier:

# Export a diagram HTML to PNG with 2x scaling (default)

diagram-design:export path/to/diagram.html --png-only --scale=2

This command invokes the Playwright workflow described in the export procedures, automatically handling the browser lifecycle and cleanup after capturing the screenshot.

Summary

• Playwright is the sole external runtime dependency required for PNG export in diagram-design, accompanied by its managed Chromium binary.
• Install using pip install playwright followed by playwright install chromium as documented in README.md lines 9-11.
• The export logic in skills/diagram-design/references/export.md (lines 55-68) validates Playwright availability before launching the Chromium-based screenshot workflow.
• No additional graphics libraries or system dependencies are required beyond the Playwright-managed browser.

Frequently Asked Questions

Is Playwright the only dependency required for PNG export in diagram-design?

Yes. According to the source code in skills/diagram-design/references/export.md, Playwright and its Chromium binary constitute the complete set of external dependencies. The system performs explicit validation at lines 55-68 to ensure Playwright is importable before attempting any browser automation.

Why does diagram-design use Playwright and Chromium instead of native graphics libraries?

The repository leverages Playwright to render HTML and SVG content through a real browser engine, ensuring CSS styles and complex SVG features display exactly as intended. This approach captures a pixel-perfect screenshot of the <svg> element using page.locator("svg").first.screenshot(), providing more accurate visual output than parser-based rasterization libraries.

How do I troubleshoot a "Playwright not found" error when exporting PNGs?

Execute the installation commands shown in README.md lines 9-11: run pip install playwright to install the Python package, then playwright install chromium to download the browser binary. The error typically occurs when the Chromium binary is missing even if the Python package is installed.

Can I configure the resolution when exporting PNG diagrams?

Yes. The export command supports a --scale parameter that maps to Playwright's device_scale_factor. As shown in the internal Python implementation, the default value is 2, but you can specify higher values (e.g., --scale=3) for increased resolution or lower values for reduced file sizes.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}