diff --git a/services/comm-services-lib/src/lib.rs b/services/comm-services-lib/src/lib.rs
--- a/services/comm-services-lib/src/lib.rs
+++ b/services/comm-services-lib/src/lib.rs
@@ -1 +1,2 @@
 pub mod database;
+pub mod tools;
diff --git a/services/comm-services-lib/src/tools.rs b/services/comm-services-lib/src/tools.rs
new file mode 100644
--- /dev/null
+++ b/services/comm-services-lib/src/tools.rs
@@ -0,0 +1,68 @@
+// colon is valid because it is used as a separator
+// in some backup service identifiers
+const VALID_IDENTIFIER_CHARS: &'static [char] = &['_', '-', '=', ':'];
+
+/// Checks if the given string is a valid identifier for an entity
+/// (e.g. backup ID, blob hash, blob holder).
+///
+/// Some popular identifier formats are considered valid, including UUID,
+/// nanoid, base64url. On the other hand, path or url-like identifiersare
+/// are not supposed to be valid
+pub fn is_valid_identifier(identifier: &str) -> bool {
+  if identifier.is_empty() {
+    return false;
+  }
+
+  identifier
+    .chars()
+    .all(|c| c.is_ascii_alphanumeric() || VALID_IDENTIFIER_CHARS.contains(&c))
+}
+
+#[cfg(test)]
+mod valid_identifier_tests {
+  use super::*;
+
+  #[test]
+  fn alphanumeric_identifier() {
+    assert!(is_valid_identifier("some_identifier_v123"));
+  }
+
+  #[test]
+  fn alphanumeric_with_colon() {
+    assert!(is_valid_identifier("some_identifier:with_colon"));
+  }
+
+  #[test]
+  fn uuid_is_valid() {
+    let example_uuid = "a2b9e4d4-8d1f-4c7f-9c3d-5f4e4e6b1d1d";
+    assert!(is_valid_identifier(example_uuid));
+  }
+
+  #[test]
+  fn base64url_is_valid() {
+    let example_base64url = "VGhlIP3-aWNrIGJyb3duIGZveCBqciAxMyBsYXp5IGRvZ_7_";
+    assert!(is_valid_identifier(example_base64url))
+  }
+
+  #[test]
+  fn standard_base64_is_invalid() {
+    let example_base64 =
+      "VGhlIP3+aWNrIGJyb3duIGZveCBqdW1wcyBvdmVyIDEzIGxhenkgZG9n/v8=";
+    assert!(!is_valid_identifier(example_base64));
+  }
+
+  #[test]
+  fn path_is_invalid() {
+    assert!(!is_valid_identifier("some/path"));
+  }
+
+  #[test]
+  fn url_is_invalid() {
+    assert!(!is_valid_identifier("https://example.com"));
+  }
+
+  #[test]
+  fn empty_is_invalid() {
+    assert!(!is_valid_identifier(""));
+  }
+}