diff --git a/.github/workflows/pages.yml b/.github/workflows/pages.yml
index 1ceed0f..7eed14f 100644
--- a/.github/workflows/pages.yml
+++ b/.github/workflows/pages.yml
@@ -7,13 +7,18 @@ name: Site
 #
 # Node 24 is a floor, not a preference: the build and prerender scripts are
 # TypeScript run straight by node, which needs its type stripping.
+#
+# The artifact also carries the coverage report, which is why a change to any
+# Go file rebuilds the site: coverage is the library's number, so it moves
+# when the library or its tests do, and narrowing these paths back to site/
+# would leave the badge reading a figure from whenever the site last changed.
 
 on:
   push:
     branches: [main]
-    paths: [site/**, examples/guide/**, .github/workflows/pages.yml]
+    paths: [site/**, examples/guide/**, "**/*.go", go.mod, .github/workflows/pages.yml]
   pull_request:
-    paths: [site/**, examples/guide/**, .github/workflows/pages.yml]
+    paths: [site/**, examples/guide/**, "**/*.go", go.mod, .github/workflows/pages.yml]
   workflow_dispatch:
 
 permissions:
@@ -28,6 +33,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v5
+      - uses: actions/setup-go@v6
+        with:
+          go-version-file: go.mod
+          check-latest: true
       - uses: actions/setup-node@v5
         with:
           node-version: 24
@@ -41,6 +50,24 @@ jobs:
         working-directory: site
         env:
           BASE_PATH: /di
+      # Written into the built site rather than served from anywhere else, so
+      # the report and the badge it links from are one deploy and cannot
+      # disagree. The profile covers di, dihttp and dislog: examples/ and
+      # benchmarks/ are separate modules and not part of the number.
+      - name: coverage report and badge, into the artifact
+        run: |
+          go test -count=1 -coverprofile=coverage.out ./...
+          go tool cover -html=coverage.out -o site/build/coverage.html
+          pct=$(go tool cover -func=coverage.out | tail -1 | awk '{print $NF}')
+          n=${pct%\%}
+          color=red
+          awk -v n="$n" 'BEGIN { exit !(n >= 90) }' && color=brightgreen
+          awk -v n="$n" 'BEGIN { exit !(n >= 80 && n < 90) }' && color=green
+          awk -v n="$n" 'BEGIN { exit !(n >= 70 && n < 80) }' && color=yellowgreen
+          awk -v n="$n" 'BEGIN { exit !(n >= 60 && n < 70) }' && color=yellow
+          printf '{"schemaVersion":1,"label":"coverage","message":"%s","color":"%s"}\n' \
+            "$pct" "$color" > site/build/coverage.json
+          echo "coverage $pct ($color)"
       - uses: actions/upload-pages-artifact@v4
         with:
           path: site/build
diff --git a/CLAUDE.md b/CLAUDE.md
index 5ca81d2..d27b578 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -592,6 +592,16 @@ reverse is caught by the fuzzer in 0.06s and *not* by the 400 seeded sequences.
 - **README code blocks are generated.** They are embedded from `examples/` with
   embedmd markers. Run `gofmt -w` on an example *before* re-embedding, or CI
   fails on the sync check.
+- **Coverage is published with the site, not to a service.** `pages.yml`
+  writes `go tool cover -html` and a shields endpoint JSON into `site/build`
+  before uploading the artifact, so the report at
+  `floatdrop.github.io/di/coverage.html` and the badge that links to it are
+  one deploy and cannot disagree. It covers `di`, `dihttp` and `dislog`: the
+  two separate modules are not part of the library's number. **That is why the
+  site workflow's path filter includes `**/*.go`** -- coverage moves when the
+  library or its tests do, and narrowing the paths back to `site/` would leave
+  the badge reading a figure from whenever the site last changed, with nothing
+  failing to say so.
 - **`examples/` and `benchmarks/` are separate modules**, each with a
   `replace ../` directive, so the root module keeps zero requires and the
   library's "no dependency outside the standard library" claim stays true.
diff --git a/README.md b/README.md
index 83e1c56..11c505a 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,7 @@
 
 [![CI](https://github.com/floatdrop/di/actions/workflows/ci.yml/badge.svg)](https://github.com/floatdrop/di/actions/workflows/ci.yml)
 [![Go Reference](https://pkg.go.dev/badge/github.com/floatdrop/di.svg)](https://pkg.go.dev/github.com/floatdrop/di)
+[![coverage](https://img.shields.io/endpoint?url=https%3A%2F%2Ffloatdrop.github.io%2Fdi%2Fcoverage.json)](https://floatdrop.github.io/di/coverage.html)
 [![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE)
 
 A dependency-injection container for Go 1.27+. Constructors are plain
diff --git a/site/README.md b/site/README.md
index 3a302bf..e36d71f 100644
--- a/site/README.md
+++ b/site/README.md
@@ -83,7 +83,7 @@ Add its id to `StepId`, then add the step to `steps` in **every** locale;
 `tsc` will not let you forget one. If it shows a new file, add the id
 to `FigureId`, the import to `src/code.ts`, and the figure to `buildFigures`.
 
-## Seven things worth knowing
+## Eight things worth knowing
 
 `src/inline-script.ts` is inlined by calling `Function.prototype.toString` on
 it, so it is cut out of its module and must close over nothing: everything it
@@ -132,3 +132,13 @@ Gravity UI's own `styles/fonts.css` pulls Inter from Google Fonts. Nothing
 third-party is on the path to rendering the page, so `src/styles/main.css`
 overrides the font stack instead; there is a comment there saying how to get
 Inter back.
+
+`site/build` is not only the site. `pages.yml` writes `coverage.html` and
+`coverage.json` into it after `npm run build` and before the artifact is
+uploaded, so the coverage report is served by the same deploy as the pages
+that link to it. Two consequences: a local `npm run build` gives a tree
+without them, and the report is the one thing on this site no local build
+reproduces; and the workflow's path filter has `**/*.go` in it, so a change to
+Go code deploys the site. Narrow that filter back to `site/` and the badge in
+the root README goes on reading a figure from whenever the site last changed,
+with nothing failing to say so.