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The Windows WSL job is the critical path of every CI run (589 to 752 s). Its checkout sits on the Windows drive, which WSL reaches over 9P, and writing node_modules there is what makes npm ci take about three minutes where the Linux job takes 23 s. The step now copies the tree onto the distro's ext4 filesystem before installing and building, as Microsoft's WSL guidance recommends for I/O-heavy work. The e2e job downloaded the full Chromium build (about 165 MB) on every run, but a headless run with no channel launches chromium-headless-shell and never opens it. `--only-shell` skips that download. Every tsconfig now lists the @types packages it uses (node, bun, vite/client, dom-speech-recognition) instead of relying on TypeScript auto-including everything under node_modules/@types. On TypeScript 5.9 this is a no-op: identical diagnostics across all 48 projects and byte-identical emitted .d.ts files. It is a prerequisite for TypeScript 7, which drops the auto-inclusion; with these lists the Go compiler passes all 48 projects, so that upgrade becomes a version bump once TypeDoc supports it. Two cache-based approaches were evaluated and rejected: an npm cache for the WSL job (npm ci is slow there because of 9P, not downloads, and a prefix-restored cache grows without bound) and a Playwright browser cache (Playwright's docs advise against it; the download is under 10 s). |
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| grid-cell.png | ||
| main.ts | ||
| mcp-app.html | ||
| package.json | ||
| README.md | ||
| screenshot.png | ||
| server.ts | ||
| tsconfig.json | ||
| tsconfig.server.json | ||
| vite.config.ts | ||
Example: Cohort Heatmap App
A demo MCP App that displays cohort retention data as an interactive heatmap, showing customer retention over time by signup month.
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MCP Client Configuration
Add to your MCP client configuration (stdio transport):
{
"mcpServers": {
"cohort-heatmap": {
"command": "npx",
"args": [
"-y",
"--silent",
"--registry=https://registry.npmjs.org/",
"@modelcontextprotocol/server-cohort-heatmap",
"--stdio"
]
}
}
}
Local Development
To test local modifications, use this configuration (replace ~/code/ext-apps with your clone path):
{
"mcpServers": {
"cohort-heatmap": {
"command": "bash",
"args": [
"-c",
"cd ~/code/ext-apps/examples/cohort-heatmap-server && npm run build >&2 && node dist/index.js --stdio"
]
}
}
}
Features
- Cohort Retention Heatmap: Color-coded grid showing retention percentages across cohorts and time periods
- Multiple Metrics: Switch between Retention %, Revenue Retention, and Active Users
- Period Types: View data by monthly or weekly intervals
- Interactive Exploration: Hover cells for detailed tooltips, click to highlight rows/columns
- Color Scale: Green (high retention) through yellow to red (low retention)
- Theme Support: Adapts to light/dark mode preferences
Running
-
Install dependencies:
npm install -
Build and start the server:
npm run start:http # for Streamable HTTP transport # OR npm run start:stdio # for stdio transport -
View using the
basic-hostexample or another MCP Apps-compatible host.
Architecture
Server (server.ts)
Exposes a single get-cohort-data tool that returns:
- Cohort rows with signup month, original user count, and retention cells
- Period headers and labels
- Configurable parameters: metric type, period type, cohort count, max periods
The tool generates synthetic cohort data using an exponential decay model with configurable retention curves per metric type.
App (src/mcp-app.tsx)
- Uses React for the heatmap visualization
- Fetches data on mount and when filters change
- Displays retention percentages in a grid with HSL color interpolation
- Shows detailed tooltips on hover with user counts and exact retention values
- Supports row/column highlighting on cell click