diff --git a/hc/lib/string.py b/hc/lib/string.py
new file mode 100644
index 00000000..f27cab85
--- /dev/null
+++ b/hc/lib/string.py
@@ -0,0 +1,38 @@
+def replace(template, ctx):
+    """Replace placeholders with their values and return the result.
+
+    Example:
+
+    >>> replace("$NAME is down", {"$NAME": "foo"})
+    foo is down
+
+    This function explicitly ignores "variable variables".
+    In this example, placeholder's value itself contains a placeholder:
+
+    >>> replace("Hello $FOO", {"$FOO": "$BAR", "$BAR": "World"})
+    Wrong: Hello World
+    Correct: Hello $BAR
+
+    >>> replace("Hello $$FOO", {"$FOO": "BAR", "$BAR": "World"})
+    Wrong: Hello World
+    Correct: Hello $BAR
+
+    In other words, this function only replaces placeholders that appear
+    in the original template. It ignores any placeholders that "emerge"
+    during string substitutions. This is done mainly to avoid unexpected
+    behavior when check names or tags contain dollar signs.
+
+    """
+
+    parts = template.split("$")
+
+    result = [parts.pop(0)]
+    for part in parts:
+        part = "$" + part
+        for placeholder, value in ctx.items():
+            if part.startswith(placeholder):
+                part = part.replace(placeholder, value, 1)
+                break
+        result.append(part)
+
+    return "".join(result)