Speedgrapher technical writing assistant and MCP server

Speedgrapher is an open source technical writing assistant for Antigravity. It pairs a side-panel Markdown editor with a Model Context Protocol server and five writing skills. You can read, edit, and review Markdown drafts in the side panel while your agent checks prose clarity, cuts corporate buzzwords and AI clichés, and audits search tags.

You get three pieces in one Go and Node.js package:

• Four-mode side panel: Switch between Reader, Editor, Reviewer, and Raw modes. You can read clean previews, edit blocks in place, resolve inline notes, or edit raw Markdown source.
• Four MCP checks: Run fog, slop, vale, and seo from your agent or shell. These tools score Gunning Fog grade level, AI slop tropes, Vale style rules, and search tags.
• Five writing skills: Guide your agent from early notes to final release with speedgrapher, ideate, draft, readability, and publish, backed by workspace rules in rules/AGENTS.md.

Quick start

1. Prerequisites

Install three tools on your machine before you build the plugin:

• Go 1.26 or newer to compile the speedgrapher binary.
• Node.js 20 or newer to run the sidecar panel.
• Vale v3 on your $PATH so the vale tool can lint your prose. Install it with brew install vale or go install github.com/errata-ai/vale/v3/cmd/vale@latest.

2. Build and install the plugin

Clone the repository and install the plugin into your local folder:

git clone https://github.com/danicat/speedgrapher.git
cd speedgrapher
make install-plugin

This step builds bin/speedgrapher, installs speedgrapher to $GOPATH/bin, and copies the plugin files into ~/.gemini/config/plugins/speedgrapher.

3. Turn it on in Antigravity

Open Customizations in the left sidebar and click the Installed tab. Find Speedgrapher and switch it On. That single toggle starts the MCP server, loads the five writing skills, and registers the side panel for your workspace.

4. Open a Markdown file

Click the [Speedgrapher](sidecar://speedgrapher/panel/) pill in chat, or type /speedgrapher at any time. When a pill links to a path with ?file=/absolute/path/to/file.md, the side panel loads that file from disk right away.

Side-panel workspace modes

Switch between four views with the [ Reader | Editor | Reviewer | Raw ] toggle in the top bar. Dark and light themes match your workspace.

1. Reader mode

Reader mode is the default view when you open a file. It renders images, tables, code blocks, alerts, task lists, math, and YAML or TOML front matter cards without highlights or inline notes in the body.

Hover over any paragraph and click 💬 Comment to open the comment popup window. If that paragraph already has notes, the popup loads them so you can edit or resolve them. On disk, Speedgrapher writes notes right below the paragraph as <!-- review: ... --> HTML comments so your feedback travels with Git commits. Click Send Comments in the top bar to stage AI rewrites in the panel, or click 💬 Send to Main Chat when you want your main chat agent to read the text.

2. Editor mode

Click any block in Editor mode to edit its Markdown in place. Press ⌘Z to undo, or press ⌘Y and ⇧⌘Z to redo your changes.

Toggle the four Editorial Lenses in the center toolbar to view Heatmap, Slop, Vale, and Fog highlights. When Heatmap is on, paragraph backgrounds tint across a seven-color scale from pristine green to bad red based on their combined scores. Click any paragraph's score pill to inspect a breakdown for that block.

Hover over any highlighted phrase to open a Before and after fix preview. From that card, you can apply a suggested fix in one click, run ✨ Rewrite with AI, or compare three rewrites in a 3-Angle Variant Tournament. In-panel AI actions use Speedgrapher's built-in Gemini or Vertex AI client and stage ✓ Accept Change and ✕ Reject diff cards in memory without writing to disk until you accept a change. If a Vale rule is too noisy for your project, click Mute Rule or + Add to Vocab on the alert card, or open ⚙️ Settings to manage AI models, rules, and custom vocabulary terms.

For blog posts and web docs, click SEO & GEO in the top bar to open the search audit popover. You can compare your human summary teaser against your search description tag, switch between Auto, Doc, and Web Page profiles, inspect the SEO and GEO checklists, and run Fix SEO to stage front matter updates.

3. Reviewer mode

Reviewer mode locks direct text editing. It displays all <!-- review: ... --> comment threads inline below their paragraphs alongside the Heatmap, Slop, Vale, and Fog lenses. You can add or edit review notes, resolve finished threads in one click, or click Send Comments to stage AI fixes for every open note.

4. Raw mode

Raw mode opens the full Markdown source in a single plain-text editor, including YAML or TOML front matter and raw HTML comment tags, with live disk sync and ⌘Z or ⌘Y undo and redo.

MCP server and command-line tool

Start the MCP server

Antigravity starts speedgrapher mcp for you through mcp_config.json. You can also run the stdio server or check the binary version in your shell:

# Start the stdio Model Context Protocol server
speedgrapher mcp

# Print the installed speedgrapher version
speedgrapher version

Run checks from your shell

Use the speedgrapher command-line tool in local scripts or build checks:

# Run fog, slop, vale, and seo in one command and print a combined JSON report
speedgrapher audit '{"path": "/absolute/path/to/article.md", "keyword": "mcp server"}'

# Call single MCP tools from the command line
speedgrapher call fog '{"path": "/absolute/path/to/article.md"}'
speedgrapher call slop '{"path": "/absolute/path/to/article.md"}'
speedgrapher call vale '{"path": "/absolute/path/to/article.md"}'
speedgrapher call seo '{"path": "/absolute/path/to/article.md", "doc_type": "page", "keyword": "mcp server"}'

Writing skills

Speedgrapher ships with five skills in skills/ that support you through every writing stage:

Build and test from source

You need Go 1.26+, Node.js 20+, and Vale v3 to build and test the project from source:

# Build bin/speedgrapher and install it to $GOPATH/bin
make build

# Build and copy the plugin to ~/.gemini/config/plugins/speedgrapher
make install-plugin

# Run the Go test suite
make test

# Write a coverage profile to coverage.out
make test-cov

# Clean build files
make clean

For AI search crawlers and coding agents, llms.txt provides a short index of the project layout, MCP tools, and writing skills.

License

You can use this project under the Apache License, Version 2.0. See LICENSE for full details.

Disclaimer

This is not an officially supported Google product.