diff --git a/cli/src/template_builder.rs b/cli/src/template_builder.rs
index 912234bf08..6940c54ed2 100644
--- a/cli/src/template_builder.rs
+++ b/cli/src/template_builder.rs
@@ -488,6 +488,11 @@ fn builtin_string_methods<'a, L: TemplateLanguage<'a>>() -> TemplateBuildMethodF
     // Not using maplit::hashmap!{} or custom declarative macro here because
     // code completion inside macro is quite restricted.
     let mut map = TemplateBuildMethodFnMap::<L, String>::new();
+    map.insert("len", |language, _build_ctx, self_property, function| {
+        template_parser::expect_no_arguments(function)?;
+        let out_property = TemplateFunction::new(self_property, |s| Ok(s.len().try_into()?));
+        Ok(language.wrap_integer(out_property))
+    });
     map.insert(
         "contains",
         |language, build_ctx, self_property, function| {
@@ -762,6 +767,12 @@ where
     O: Template<()> + Clone + 'a,
 {
     let property = match function.name {
+        "len" => {
+            template_parser::expect_no_arguments(function)?;
+            let out_property =
+                TemplateFunction::new(self_property, |items| Ok(items.len().try_into()?));
+            language.wrap_integer(out_property)
+        }
         "join" => {
             let [separator_node] = template_parser::expect_exact_arguments(function)?;
             let separator = expect_template_expression(language, build_ctx, separator_node)?;
@@ -789,6 +800,12 @@ where
     O: Clone + 'a,
 {
     let property = match function.name {
+        "len" => {
+            template_parser::expect_no_arguments(function)?;
+            let out_property =
+                TemplateFunction::new(self_property, |items| Ok(items.len().try_into()?));
+            language.wrap_integer(out_property)
+        }
         // No "join"
         "map" => build_map_operation(language, build_ctx, self_property, function, wrap_item)?,
         _ => return Err(TemplateParseError::no_such_method("List", function)),
@@ -1536,6 +1553,9 @@ mod tests {
             language.wrap_string(Literal("sep".to_owned()))
         });
 
+        insta::assert_snapshot!(env.render_ok(r#""".lines().len()"#), @"0");
+        insta::assert_snapshot!(env.render_ok(r#""a\nb\nc".lines().len()"#), @"3");
+
         insta::assert_snapshot!(env.render_ok(r#""".lines().join("|")"#), @"");
         insta::assert_snapshot!(env.render_ok(r#""a\nb\nc".lines().join("|")"#), @"a|b|c");
         // Null separator
@@ -1633,6 +1653,10 @@ mod tests {
             language.wrap_string(Literal("description 1".to_owned()))
         });
 
+        insta::assert_snapshot!(env.render_ok(r#""".len()"#), @"0");
+        insta::assert_snapshot!(env.render_ok(r#""foo".len()"#), @"3");
+        insta::assert_snapshot!(env.render_ok(r#""💩".len()"#), @"4");
+
         insta::assert_snapshot!(env.render_ok(r#""fooo".contains("foo")"#), @"true");
         insta::assert_snapshot!(env.render_ok(r#""foo".contains("fooo")"#), @"false");
         insta::assert_snapshot!(env.render_ok(r#"description.contains("description")"#), @"true");
diff --git a/cli/tests/test_commit_template.rs b/cli/tests/test_commit_template.rs
index 13eda0c4fa..6f424cf3bc 100644
--- a/cli/tests/test_commit_template.rs
+++ b/cli/tests/test_commit_template.rs
@@ -26,17 +26,18 @@ fn test_log_parents() {
     test_env.jj_cmd_ok(&repo_path, &["new", "@-"]);
     test_env.jj_cmd_ok(&repo_path, &["new", "@", "@-"]);
 
-    let template = r#"commit_id ++ "\nP: " ++ parents.map(|c| c.commit_id()) ++ "\n""#;
+    let template =
+        r#"commit_id ++ "\nP: " ++ parents.len() ++ " " ++ parents.map(|c| c.commit_id()) ++ "\n""#;
     let stdout = test_env.jj_cmd_success(&repo_path, &["log", "-T", template]);
     insta::assert_snapshot!(stdout, @r###"
     @    c067170d4ca1bc6162b64f7550617ec809647f84
-    ├─╮  P: 4db490c88528133d579540b6900b8098f0c17701 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    ├─╮  P: 2 4db490c88528133d579540b6900b8098f0c17701 230dd059e1b059aefc0da06a2e5a7dbf22362f22
     ◉ │  4db490c88528133d579540b6900b8098f0c17701
-    ├─╯  P: 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    ├─╯  P: 1 230dd059e1b059aefc0da06a2e5a7dbf22362f22
     ◉  230dd059e1b059aefc0da06a2e5a7dbf22362f22
-    │  P: 0000000000000000000000000000000000000000
+    │  P: 1 0000000000000000000000000000000000000000
     ◉  0000000000000000000000000000000000000000
-       P:
+       P: 0
     "###);
 
     let template = r#"parents.map(|c| c.commit_id().shortest(4))"#;
diff --git a/docs/templates.md b/docs/templates.md
index 595b2a142f..c9424f6033 100644
--- a/docs/templates.md
+++ b/docs/templates.md
@@ -105,6 +105,7 @@ No methods are defined.
 A list can be implicitly converted to `Boolean`. The following methods are
 defined.
 
+* `.len() -> Integer`: Number of elements in the list.
 * `.join(separator: Template) -> Template`: Concatenate elements with
   the given `separator`.
 * `.map(|item| expression) -> ListTemplate`: Apply template `expression`
@@ -164,6 +165,7 @@ The following methods are defined.
 A string can be implicitly converted to `Boolean`. The following methods are
 defined.
 
+* `.len() -> Integer`: Length in UTF-8 bytes.
 * `.contains(needle: Template) -> Boolean`
 * `.first_line() -> String`
 * `.lines() -> List<String>`: Split into lines excluding newline characters.