diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
index 35c12179a..244dcf524 100644
--- a/.github/workflows/docs.yml
+++ b/.github/workflows/docs.yml
@@ -77,6 +77,8 @@ jobs:
       - name: Build site
         working-directory: docs
         run: npm run build
+        env:
+          DOCS_BASE: /MTConnect.NET/
 
       # Upload the built artifact only on the deploy path. PR builds stop
       # after the build step (success / failure surfaces in the check).
diff --git a/docs/.vitepress/config.ts b/docs/.vitepress/config.ts
index 6f53a2394..bf8ce7183 100644
--- a/docs/.vitepress/config.ts
+++ b/docs/.vitepress/config.ts
@@ -31,10 +31,8 @@ export default withMermaid(
     // overriding here is unnecessary unless we deploy from elsewhere.
     // outDir: '.vitepress/dist',
 
-    // Base path. Defaults to '/'. If GitHub Pages publishes under a project
-    // path (e.g. `/MTConnect.NET/`), this will need to be set at deploy
-    // time. Left as the default for now.
-    // base: '/',
+    // Defaults to '/' for local dev; CI sets DOCS_BASE for GitHub Pages.
+    base: process.env.DOCS_BASE ?? '/',
 
     cleanUrls: true,
 
@@ -226,6 +224,7 @@ export default withMermaid(
           {
             text: 'Repository development',
             items: [
+              { text: 'Documentation site', link: '/development/docs-site' },
               { text: 'Release builder', link: '/development/builder' },
             ],
           },
diff --git a/docs/development/docs-site.md b/docs/development/docs-site.md
new file mode 100644
index 000000000..dfdad9271
--- /dev/null
+++ b/docs/development/docs-site.md
@@ -0,0 +1,64 @@
+# Documentation site
+
+The documentation site you are reading is built with [VitePress](https://vitepress.dev/) from the `docs/` directory in the repository. This page covers how to build it locally and how the production deploy resolves its public base path.
+
+## Local development
+
+```
+cd docs
+npm ci
+npm run dev
+```
+
+The dev server hot-reloads markdown edits, theme tweaks, and config changes. It serves from `http://localhost:5173/` with no path prefix.
+
+## Production build
+
+```
+cd docs
+npm run build
+```
+
+The build emits a static site under `docs/.vitepress/dist/`. Preview it with `npm run preview`, which serves the built artifact at the same `localhost:5173` origin.
+
+## Base path—`DOCS_BASE`
+
+VitePress emits asset URLs (CSS, JavaScript, fonts, images) at build time using its `base` configuration. The shipped config reads `base` from the `DOCS_BASE` environment variable and defaults to `/` when unset:
+
+```ts
+// docs/.vitepress/config.ts
+base: process.env.DOCS_BASE ?? '/',
+```
+
+Why it matters: when the built site is served from a sub-path—for example GitHub Pages at `https://trakhound.github.io/MTConnect.NET/`—the asset URLs must include the `/MTConnect.NET/` prefix or the browser fetches `https://trakhound.github.io/assets/…` and 404s every asset, leaving an unstyled raw-HTML render. The base must match the public deploy URL at the time `vitepress build` runs; rewriting it post-build is not supported by VitePress.
+
+| Environment | `DOCS_BASE` value | Resolved asset URL |
+| --- | --- | --- |
+| Local dev (`npm run dev` / `npm run preview`) | unset (defaults to `/`) | `http://localhost:5173/assets/…` |
+| GitHub Pages production build | `/MTConnect.NET/` | `https://trakhound.github.io/MTConnect.NET/assets/…` |
+| Custom deploy target at `https://docs.example.com/mtconnect/` | `/mtconnect/` | `https://docs.example.com/mtconnect/assets/…` |
+| Custom deploy target at a root domain like `https://docs.example.com/` | unset or `/` | `https://docs.example.com/assets/…` |
+
+The variable is read by Node at the moment `vitepress build` starts, so any deployment pipeline can override it by exporting the variable in the build step.
+
+## How CI sets the base
+
+`.github/workflows/docs.yml` builds the site on every push and pull request, and deploys the artifact to GitHub Pages on merges to `master`. The build step passes `DOCS_BASE: /MTConnect.NET/` explicitly:
+
+```yaml
+- name: Build site
+  working-directory: docs
+  run: npm run build
+  env:
+    DOCS_BASE: /MTConnect.NET/
+```
+
+A fork or third-party deploy that hosts the same documentation under a different URL—for example a vendor preview hosted at `/preview/`—sets `DOCS_BASE: /preview/` on its own build step. No code changes are needed.
+
+## Diagnosing a styling break on a live deploy
+
+The classic symptom of a base mismatch is a deployed page that renders as raw HTML: title and tagline run together without spacing, the `Search` button reads `SearchK` because the keyboard-shortcut hint sits adjacent to the label without CSS spacing, and the nav links concatenate without separators. Check the page's HTML source for `<link rel="stylesheet">` and `<script type="module">` tags; if their `href` / `src` attributes do not include the deploy URL's path prefix, the build was produced with the wrong `DOCS_BASE`.
+
+## See also
+
+- [Release builder](/development/builder)—the in-tree tool that assembles binary release artifacts (NuGet packages, installers, Docker images). Distinct from the documentation site build covered above.