diff --git a/crates/ruff_linter/src/checkers/noqa.rs b/crates/ruff_linter/src/checkers/noqa.rs
index e893551dfcd4b..f392f568ccfdf 100644
--- a/crates/ruff_linter/src/checkers/noqa.rs
+++ b/crates/ruff_linter/src/checkers/noqa.rs
@@ -43,7 +43,8 @@ pub(crate) fn check_noqa(
     let exemption = FileExemption::from(&file_noqa_directives);
 
     // Extract all `noqa` directives.
-    let mut noqa_directives = NoqaDirectives::from_commented_ranges(comment_ranges, path, locator);
+    let mut noqa_directives =
+        NoqaDirectives::from_commented_ranges(comment_ranges, &settings.external, path, locator);
 
     // Indices of diagnostics that were ignored by a `noqa` directive.
     let mut ignored_diagnostics = vec![];
diff --git a/crates/ruff_linter/src/noqa.rs b/crates/ruff_linter/src/noqa.rs
index 1653d3f3f5538..ebfc40823f9fa 100644
--- a/crates/ruff_linter/src/noqa.rs
+++ b/crates/ruff_linter/src/noqa.rs
@@ -36,7 +36,7 @@ pub fn generate_noqa_edits(
     let file_directives =
         FileNoqaDirectives::extract(locator.contents(), comment_ranges, external, path, locator);
     let exemption = FileExemption::from(&file_directives);
-    let directives = NoqaDirectives::from_commented_ranges(comment_ranges, path, locator);
+    let directives = NoqaDirectives::from_commented_ranges(comment_ranges, external, path, locator);
     let comments = find_noqa_comments(diagnostics, locator, &exemption, &directives, noqa_line_for);
     build_noqa_edits_by_diagnostic(comments, locator, line_ending)
 }
@@ -183,7 +183,7 @@ impl<'a> Directive<'a> {
         // Extract, e.g., the `401` in `F401`.
         let suffix = line[prefix..]
             .chars()
-            .take_while(char::is_ascii_digit)
+            .take_while(char::is_ascii_alphanumeric)
             .count();
         if prefix > 0 && suffix > 0 {
             Some(&line[..prefix + suffix])
@@ -550,7 +550,7 @@ impl<'a> ParsedFileExemption<'a> {
         // Extract, e.g., the `401` in `F401`.
         let suffix = line[prefix..]
             .chars()
-            .take_while(char::is_ascii_digit)
+            .take_while(char::is_ascii_alphanumeric)
             .count();
         if prefix > 0 && suffix > 0 {
             Some(&line[..prefix + suffix])
@@ -623,7 +623,7 @@ fn add_noqa_inner(
         FileNoqaDirectives::extract(locator.contents(), comment_ranges, external, path, locator);
     let exemption = FileExemption::from(&directives);
 
-    let directives = NoqaDirectives::from_commented_ranges(comment_ranges, path, locator);
+    let directives = NoqaDirectives::from_commented_ranges(comment_ranges, external, path, locator);
 
     let comments = find_noqa_comments(diagnostics, locator, &exemption, &directives, noqa_line_for);
 
@@ -897,7 +897,7 @@ pub(crate) struct NoqaDirectiveLine<'a> {
     pub(crate) directive: Directive<'a>,
     /// The codes that are ignored by the directive.
     pub(crate) matches: Vec<NoqaCode>,
-    // Whether the directive applies to range.end
+    /// Whether the directive applies to `range.end`.
     pub(crate) includes_end: bool,
 }
 
@@ -916,6 +916,7 @@ pub(crate) struct NoqaDirectives<'a> {
 impl<'a> NoqaDirectives<'a> {
     pub(crate) fn from_commented_ranges(
         comment_ranges: &CommentRanges,
+        external: &[String],
         path: &Path,
         locator: &'a Locator<'a>,
     ) -> Self {
@@ -930,7 +931,29 @@ impl<'a> NoqaDirectives<'a> {
                     warn!("Invalid `# noqa` directive on {path_display}:{line}: {err}");
                 }
                 Ok(Some(directive)) => {
-                    // noqa comments are guaranteed to be single line.
+                    if let Directive::Codes(codes) = &directive {
+                        // Warn on invalid rule codes.
+                        for code in &codes.codes {
+                            // Ignore externally-defined rules.
+                            if !external
+                                .iter()
+                                .any(|external| code.as_str().starts_with(external))
+                            {
+                                if Rule::from_code(
+                                    get_redirect_target(code.as_str()).unwrap_or(code.as_str()),
+                                )
+                                .is_err()
+                                {
+                                    #[allow(deprecated)]
+                                    let line = locator.compute_line_index(range.start());
+                                    let path_display = relativize_path(path);
+                                    warn!("Invalid rule code provided to `# noqa` at {path_display}:{line}: {code}");
+                                }
+                            }
+                        }
+                    }
+
+                    // `# noqa` comments are guaranteed to be single line.
                     let range = locator.line_range(range.start());
                     directives.push(NoqaDirectiveLine {
                         range,
@@ -1193,6 +1216,18 @@ mod tests {
         assert_debug_snapshot!(Directive::try_extract(source, TextSize::default()));
     }
 
+    #[test]
+    fn noqa_squashed_codes() {
+        let source = "# noqa: F401F841";
+        assert_debug_snapshot!(Directive::try_extract(source, TextSize::default()));
+    }
+
+    #[test]
+    fn noqa_empty_comma() {
+        let source = "# noqa: F401,,F841";
+        assert_debug_snapshot!(Directive::try_extract(source, TextSize::default()));
+    }
+
     #[test]
     fn noqa_invalid_suffix() {
         let source = "# noqa[F401]";
diff --git a/crates/ruff_linter/src/snapshots/ruff_linter__noqa__tests__noqa_empty_comma.snap b/crates/ruff_linter/src/snapshots/ruff_linter__noqa__tests__noqa_empty_comma.snap
new file mode 100644
index 0000000000000..7a83ed9db2271
--- /dev/null
+++ b/crates/ruff_linter/src/snapshots/ruff_linter__noqa__tests__noqa_empty_comma.snap
@@ -0,0 +1,23 @@
+---
+source: crates/ruff_linter/src/noqa.rs
+expression: "Directive::try_extract(source, TextSize::default())"
+---
+Ok(
+    Some(
+        Codes(
+            Codes {
+                range: 0..18,
+                codes: [
+                    Code {
+                        code: "F401",
+                        range: 8..12,
+                    },
+                    Code {
+                        code: "F841",
+                        range: 14..18,
+                    },
+                ],
+            },
+        ),
+    ),
+)
diff --git a/crates/ruff_linter/src/snapshots/ruff_linter__noqa__tests__noqa_squashed_codes.snap b/crates/ruff_linter/src/snapshots/ruff_linter__noqa__tests__noqa_squashed_codes.snap
new file mode 100644
index 0000000000000..8a6adc1cc7a11
--- /dev/null
+++ b/crates/ruff_linter/src/snapshots/ruff_linter__noqa__tests__noqa_squashed_codes.snap
@@ -0,0 +1,19 @@
+---
+source: crates/ruff_linter/src/noqa.rs
+expression: "Directive::try_extract(source, TextSize::default())"
+---
+Ok(
+    Some(
+        Codes(
+            Codes {
+                range: 0..16,
+                codes: [
+                    Code {
+                        code: "F401F841",
+                        range: 8..16,
+                    },
+                ],
+            },
+        ),
+    ),
+)