diff --git a/.nvmrc b/.nvmrc
new file mode 100644
index 000000000..209e3ef4b
--- /dev/null
+++ b/.nvmrc
@@ -0,0 +1 @@
+20
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 7c7c57d04..dad2d10a6 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -24,7 +24,7 @@ Prerequisites:
 
 - Docker and Docker Compose
 - Java 21
-- Node.js and `pnpm`
+- Node.js 20 or 22 (see `.nvmrc`; Node 25+ currently breaks jsdom-based web tests — #991) and `pnpm`
 
 Start the local stack:
 
diff --git a/web/package.json b/web/package.json
index ac1340ec4..a1d9924c1 100644
--- a/web/package.json
+++ b/web/package.json
@@ -92,5 +92,8 @@
     "typescript": "^5.7.0",
     "vite": "^6.4.3",
     "vitest": "^4.1.11"
+  },
+  "engines": {
+    "node": ">=20 <25"
   }
 }