diff --git a/lib/src/spec/mod.rs b/lib/src/spec/mod.rs
index 15b896b5..5970128e 100644
--- a/lib/src/spec/mod.rs
+++ b/lib/src/spec/mod.rs
@@ -85,7 +85,7 @@ impl Spec {
     ///
     /// Automatically detects whether the file is:
     /// - A `.kdl` or `.usage.kdl` file containing a raw spec
-    /// - A script file with embedded `# USAGE:` comments
+    /// - A script file with embedded `#USAGE` comments
     ///
     /// If `bin` is not specified in the spec, it defaults to the filename.
     #[must_use = "parsing result should be used"]
@@ -107,13 +107,12 @@ impl Spec {
     }
     /// Parse a spec from a script file's embedded USAGE comments.
     ///
-    /// Extracts the spec from comment lines starting with `# USAGE:` or `// USAGE:`.
+    /// Extracts the spec from comment lines marked with `#USAGE`, `//USAGE`,
+    /// `::USAGE`, or their `[USAGE]` variants.
     /// If `bin` is not specified in the spec, it defaults to the filename.
     #[must_use = "parsing result should be used"]
     pub fn parse_script(file: &Path) -> Result<Spec, UsageErr> {
-        let raw = extract_usage_from_comments(&file::read_to_string(file)?);
-        let ctx = ParsingContext::new(file, &raw);
-        let mut spec = Self::parse(&ctx, &raw)?;
+        let mut spec = Self::parse_script_with_path(&file::read_to_string(file)?, file)?;
         if spec.bin.is_empty() {
             spec.bin = file
                 .file_name()
@@ -127,6 +126,24 @@ impl Spec {
         Ok(spec)
     }
 
+    /// Parse a spec from a script string's embedded USAGE comments.
+    ///
+    /// Extracts the spec from comment lines marked with `#USAGE`, `//USAGE`,
+    /// `::USAGE`, or their `[USAGE]` variants. Unlike [`Self::parse_script`],
+    /// this function cannot infer `bin` or `name` from a filename. Relative
+    /// `include` paths are rejected because there is no source path to resolve
+    /// them against; absolute `include` paths remain supported.
+    #[must_use = "parsing result should be used"]
+    pub fn parse_script_str(input: &str) -> Result<Spec, UsageErr> {
+        Self::parse_script_with_path(input, Path::new(""))
+    }
+
+    fn parse_script_with_path(input: &str, file: &Path) -> Result<Spec, UsageErr> {
+        let raw = extract_usage_from_comments(input);
+        let ctx = ParsingContext::new(file, &raw);
+        Self::parse(&ctx, &raw)
+    }
+
     #[deprecated]
     pub fn parse_spec(input: &str) -> Result<Spec, UsageErr> {
         Self::parse(&Default::default(), input)
@@ -224,10 +241,12 @@ impl Spec {
                             .file
                             .parent()
                             .ok_or_else(|| {
-                                ctx.build_err(
-                                    format!("cannot get parent of {}", ctx.file.display()),
-                                    node.span(),
-                                )
+                                let msg = if ctx.file.as_os_str().is_empty() {
+                                    "relative includes require a source file".to_string()
+                                } else {
+                                    format!("cannot get parent of {}", ctx.file.display())
+                                };
+                                ctx.build_err(msg, node.span())
                             })?
                             .join(file),
                         false => file.to_path_buf(),
@@ -982,4 +1001,35 @@ example "demo --version"
         );
         assert!(output.contains("example \"demo --version\""));
     }
+
+    #[test]
+    fn test_parse_script_str() {
+        let spec = Spec::parse_script_str(
+            r#"
+#!/bin/bash
+#USAGE bin "test"
+#USAGE flag "--foo" help="test"
+echo "hello"
+            "#,
+        )
+        .unwrap();
+
+        assert_eq!(spec.bin, "test");
+        assert_eq!(spec.name, "test");
+        assert_eq!(spec.cmd.flags.len(), 1);
+        assert_eq!(spec.cmd.flags[0].long, ["foo"]);
+    }
+
+    #[test]
+    fn test_parse_script_str_rejects_relative_includes() {
+        let err = Spec::parse_script_str(r#"#USAGE include file="relative.usage.kdl""#)
+            .expect_err("relative includes need a source path");
+
+        match err {
+            UsageErr::InvalidInput(msg, _, _) => {
+                assert_eq!(msg, "relative includes require a source file");
+            }
+            err => panic!("unexpected error: {err:?}"),
+        }
+    }
 }