diff --git a/string.libsonnet b/string.libsonnet
index 6655981..4245c6e 100644
--- a/string.libsonnet
+++ b/string.libsonnet
@@ -12,6 +12,15 @@ local d = import 'github.com/jsonnet-libs/docsonnet/doc-util/main.libsonnet';
   // character and thereby will unlikely be in a valid key by accident. Only when we include it.
   local BelRune = std.char(7),
 
+  '#capitalize':: d.fn(
+    |||
+      `capitalize` will uppercase the first letter of string.
+    |||,
+    [d.arg('str', d.T.string)]
+  ),
+  capitalize(str): if std.length(str) > 0 then
+    std.asciiUpper(str[0]) + std.substr(str, 1, std.length(str) - 1) else '',
+
   '#splitEscape':: d.fn(
     |||
       `split` works the same as `std.split` but with support for escaping the dividing
diff --git a/test/string_test.jsonnet b/test/string_test.jsonnet
new file mode 100644
index 0000000..43a9435
--- /dev/null
+++ b/test/string_test.jsonnet
@@ -0,0 +1,19 @@
+local xtd = import '../main.libsonnet';
+local test = import 'github.com/jsonnet-libs/testonnet/main.libsonnet';
+
+test.new(std.thisFile)
++ test.case.new(
+  name='empty',
+  test=test.expect.eq(
+    actual=xtd.string.capitalize(''),
+    expected='',
+  )
+)
+
++ test.case.new(
+  name='abc',
+  test=test.expect.eq(
+    actual=xtd.string.capitalize('abc'),
+    expected='Abc',
+  )
+)