diff --git a/crates/engine/src/cmd/help.rs b/crates/engine/src/cmd/help.rs
index c6f315f30..996817ce3 100644
--- a/crates/engine/src/cmd/help.rs
+++ b/crates/engine/src/cmd/help.rs
@@ -20,7 +20,8 @@ fn sibling(s: &mut Session, p: &Value) -> Result<Value> {
 fn docs(s: &mut Session, p: &Value) -> Result<Value> {
     let page = match str_p(p, "page").unwrap_or("help") {
         "scripting" => "docs/control-protocol.md",
-        "expressions" => "docs/expressions.md",
+        // The reader-facing expression reference is not written yet: the closest page is the parity notes.
+        "expressions" => "docs/scripting-parity.md",
         "effects" => "docs/effects.md",
         "agents" => "docs/agents.md",
         _ => "README.md",
diff --git a/crates/engine/src/tests/session.rs b/crates/engine/src/tests/session.rs
index 19bf93090..b253640e7 100644
--- a/crates/engine/src/tests/session.rs
+++ b/crates/engine/src/tests/session.rs
@@ -497,6 +497,19 @@ fn help_links_emit_urls() {
     assert_eq!(s.execute("help.github", json!({})).unwrap()["url"], "https://github.com/storytold/effectcraft");
 }
 
+/// Every Help ▸ documentation page opens a file that is in the repository (#2696: Expression Reference opened a 404).
+#[test]
+fn help_docs_pages_exist_in_the_repository() {
+    let root = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../..");
+    for page in [None, Some("help"), Some("scripting"), Some("expressions"), Some("effects"), Some("agents")] {
+        let mut s = Session::default();
+        let params = page.map_or_else(|| json!({}), |p| json!({"page": p}));
+        let url = s.execute("help.docs", params).unwrap()["url"].as_str().unwrap().to_owned();
+        let path = url.strip_prefix("https://github.com/storytold/effectcraft/blob/main/").unwrap_or_else(|| panic!("{page:?}: {url}"));
+        assert!(root.join(path).is_file(), "{page:?} opens {url}, which is not in the repository");
+    }
+}
+
 #[test]
 fn time_navigation() {
     let mut s = demo();