diff --git a/crates/bindings/npm/.gitignore b/crates/bindings/npm/.gitignore
new file mode 100644
index 0000000..c2658d7
--- /dev/null
+++ b/crates/bindings/npm/.gitignore
@@ -0,0 +1 @@
+node_modules/
diff --git a/crates/bindings/npm/build.sh b/crates/bindings/npm/build.sh
index a73e851..f704e64 100755
--- a/crates/bindings/npm/build.sh
+++ b/crates/bindings/npm/build.sh
@@ -44,6 +44,17 @@ done
 mv "$out/node/catena.js" "$out/node/catena.cjs"
 mv "$out/node/catena.d.ts" "$out/node/catena.d.cts"
 
+# The declarations are hand-written, so nothing but a type checker would
+# notice them going wrong. Skipped where TypeScript is not installed rather
+# than made a dependency of building at all.
+if [ -x node_modules/.bin/tsc ]; then
+	node_modules/.bin/tsc --noEmit --strict --target es2022 --module es2022 \
+		--moduleResolution bundler typecheck.ts
+	echo "declarations typecheck"
+else
+	echo "skipped typecheck: npm install --no-save typescript" >&2
+fi
+
 sed "s/@VERSION@/$version/" package.json.in >"$out/package.json"
 cp README.md "$out/README.md"
 cp ../LICENSE "$out/LICENSE"
diff --git a/crates/bindings/npm/typecheck.ts b/crates/bindings/npm/typecheck.ts
new file mode 100644
index 0000000..fef0c35
--- /dev/null
+++ b/crates/bindings/npm/typecheck.ts
@@ -0,0 +1,38 @@
+// Checked, not run: every line here must compile against the declarations the
+// package ships. A binding whose types say `any` is one TypeScript cannot
+// check, and nothing else would notice.
+import {
+  chunkMarkdown, scrub, countTokens, parseSubtitles, packCues,
+  splitCollection, fuseHits, identify,
+  type Chunk, type Cue, type Section, type Hit, type Doc,
+} from "./dist/web/catena.js";
+
+const chunks: Chunk[] = chunkMarkdown("# One\n\nbody\n", 512, 64, 50, 768);
+const page: number | null = chunks[0].page;
+const chapter: string | null = chunks[0].chapter;
+const flags: string[] = chunks[0].flags;
+
+const clean: string = scrub("# One\n", true);
+const tokens: number = countTokens(clean);
+
+const cues: Cue[] = parseSubtitles("1\n00:00:01,000 --> 00:00:04,000\nline\n\n");
+const start: number = cues[0].start;
+const packed: Chunk[] = packCues(cues, 75, 512);
+
+const works: Section[] = splitCollection("# One\n\nbody\n");
+const slug: string = works[0].slug;
+
+const hits: Hit[] = [{ v: 1, id: "a", channel: "vec", rank: 1, score: 0.5, payload: {} }];
+const fused: Hit[] = fuseHits(hits, 60, { vec: 2, fts: 1 }, 10);
+
+const doc: Doc = identify("book.pdf", new Uint8Array([0x25, 0x50]));
+const kind: string = doc.kind;
+const notes: string[] = doc.notes;
+
+// Optional arguments really are optional.
+chunkMarkdown("x");
+parseSubtitles("x");
+packCues(cues);
+fuseHits(hits);
+
+export const checked = [page, chapter, flags, clean, tokens, start, packed, slug, fused, kind, notes];