diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index c7a67127..1564102a 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -2,3 +2,8 @@
 **Vulnerability:** CSV formula injection mitigation was naive, missing leading whitespace, tabs, and newlines.
 **Learning:** Checking `/^[=+\-@]/` is not sufficient, as OWASP states that spaces and tabs before the formula triggers will also execute the formula in applications like Excel.
 **Prevention:** Use a regex that allows leading whitespace (e.g. `/^[\s\uFEFF\xA0]*[=+\-@\t\r\n]/`) and include standalone tabs or new lines which are also injection vectors.
+
+## 2025-06-22 - URL Parsing Length Limit
+**Vulnerability:** Unbounded URL inputs across TypeScript, Rust, and Python entry points.
+**Learning:** Regular expressions and URL parsers can spend avoidable CPU or memory on oversized attacker-controlled strings.
+**Prevention:** Cap URL length to the product-supported maximum before handing user input to regex or URL parsers.
diff --git a/apps/desktop/src-tauri/src/main.rs b/apps/desktop/src-tauri/src/main.rs
index 2de7adde..ee47cc26 100644
--- a/apps/desktop/src-tauri/src/main.rs
+++ b/apps/desktop/src-tauri/src/main.rs
@@ -34,6 +34,7 @@ const ANALYSIS_WAIT_POLL: Duration = Duration::from_millis(50);
 const AUDIO_EXTENSIONS: [&str; 4] = ["wav", "mp3", "flac", "m4a"];
 const MISSING_ANALYSIS_PYTHON: &str = "__bandscope_missing_analysis_python__";
 const YOUTUBE_IMPORT_TIMEOUT: Duration = Duration::from_secs(120);
+const MAX_YOUTUBE_URL_LENGTH: usize = 2000;
 
 impl Default for AppState {
     fn default() -> Self {
@@ -1057,6 +1058,10 @@ async fn import_youtube_url(
 }
 
 fn is_supported_youtube_url(url: &str) -> bool {
+    if url.len() > MAX_YOUTUBE_URL_LENGTH {
+        return false;
+    }
+
     let parsed_url = match url::Url::parse(url) {
         Ok(u) => u,
         Err(_) => return false,
@@ -1366,6 +1371,11 @@ mod tests {
         assert!(!is_supported_youtube_url(
             "https://youtube.com/watch?v=abc123DEF45&v=def456GHI78"
         ));
+        let oversized_url = format!(
+            "https://youtube.com/watch?v=abc123DEF45&x={}",
+            "a".repeat(MAX_YOUTUBE_URL_LENGTH)
+        );
+        assert!(!is_supported_youtube_url(&oversized_url));
         assert!(!is_supported_youtube_url("https://youtu.be/abc123"));
         assert!(!is_supported_youtube_url("https://youtu.be/abc123DEF4!"));
     }
diff --git a/apps/desktop/src/App.test.tsx b/apps/desktop/src/App.test.tsx
index c039dfba..7e2b6d8a 100644
--- a/apps/desktop/src/App.test.tsx
+++ b/apps/desktop/src/App.test.tsx
@@ -223,6 +223,12 @@ describe("App", () => {
     expect(sourceControls).toHaveTextContent(/Import YouTube/i);
   });
 
+  it("caps the YouTube URL input before import-path validation", () => {
+    render(<App />);
+
+    expect(screen.getByRole("textbox", { name: /YouTube URL/i })).toHaveAttribute("maxlength", "2000");
+  });
+
   it("renders the loaded song as a dark rehearsal command board", async () => {
     mockLoadProject.mockResolvedValueOnce(succeededResult().result);
     render(<App />);
diff --git a/apps/desktop/src/App.tsx b/apps/desktop/src/App.tsx
index 24f5fb09..b633b662 100644
--- a/apps/desktop/src/App.tsx
+++ b/apps/desktop/src/App.tsx
@@ -35,6 +35,7 @@ import {
   importYoutubeUrl,
   isSupportedYoutubeUrl,
   loadProject,
+  MAX_YOUTUBE_URL_LENGTH,
   saveProject,
   subscribeToAnalysisJobUpdates,
   selectLocalAudioSource,
@@ -605,6 +606,7 @@ export function App() {
                       type="text"
                       placeholder={t("youtubePlaceholder")}
                       value={youtubeUrl}
+                      maxLength={MAX_YOUTUBE_URL_LENGTH}
                       onChange={(e) => setYoutubeUrl(e.target.value)}
                       disabled={analysisInFlight || isStarting || isImporting}
                       className="h-10 flex-1 border-0 bg-transparent text-slate-100 placeholder:text-slate-500 focus-visible:ring-cyan-300"
diff --git a/apps/desktop/src/lib/analysis.test.ts b/apps/desktop/src/lib/analysis.test.ts
index b443b41f..e3347d1f 100644
--- a/apps/desktop/src/lib/analysis.test.ts
+++ b/apps/desktop/src/lib/analysis.test.ts
@@ -1,6 +1,11 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
 import { createDemoAnalysisJobRequest, createDemoRehearsalSong } from "@bandscope/shared-types";
-import { getAnalysisJobStatus, importYoutubeUrl, startAnalysisJob } from "./analysis";
+import {
+  MAX_YOUTUBE_URL_LENGTH,
+  getAnalysisJobStatus,
+  importYoutubeUrl,
+  startAnalysisJob
+} from "./analysis";
 
 type TauriWindow = Window & {
   __TAURI_INTERNALS__?: unknown;
@@ -196,6 +201,23 @@ describe("analysis bridge", () => {
     });
   });
 
+  it("rejects oversized YouTube URLs before crossing the Tauri bridge", async () => {
+    tauriWindow.__TAURI_INVOKE__ = vi.fn();
+    const urlPrefix = "https://youtube.com/watch?v=4ozX4yFUC34&x=";
+    const oversizedUrl = `${urlPrefix}${"a".repeat(MAX_YOUTUBE_URL_LENGTH - urlPrefix.length + 1)}`;
+
+    const selection = await importYoutubeUrl(oversizedUrl);
+
+    expect(tauriWindow.__TAURI_INVOKE__).not.toHaveBeenCalled();
+    expect(selection).toEqual({
+      ok: false,
+      error: {
+        code: "invalid_request",
+        message: "Only standard YouTube URLs are supported."
+      }
+    });
+  });
+
   it.each([
     "https://youtube.com/watch?v=too-short",
     "https://youtube.com/watch?v=4ozX4yFUC3!",
diff --git a/apps/desktop/src/lib/analysis.ts b/apps/desktop/src/lib/analysis.ts
index f6ee7c00..bb750b34 100644
--- a/apps/desktop/src/lib/analysis.ts
+++ b/apps/desktop/src/lib/analysis.ts
@@ -43,6 +43,9 @@ const SAFE_LOCAL_AUDIO_MESSAGES = new Set([
   "Could not prepare the local temp workspace."
 ]);
 const YOUTUBE_VIDEO_ID_PATTERN = /^[A-Za-z0-9_-]{11}$/;
+const MAX_YOUTUBE_URL_LENGTH = 2000;
+
+export { MAX_YOUTUBE_URL_LENGTH };
 
 /** Documented. */
 export type LocalAudioSelectionResult =
@@ -74,6 +77,9 @@ export function isSupportedYoutubeUrl(rawUrl: unknown): rawUrl is string {
   if (typeof rawUrl !== "string") {
     return false;
   }
+  if (rawUrl.length > MAX_YOUTUBE_URL_LENGTH) {
+    return false;
+  }
 
   let parsedUrl: URL;
   try {
diff --git a/services/analysis-engine/src/bandscope_analysis/youtube.py b/services/analysis-engine/src/bandscope_analysis/youtube.py
index aa27d6f7..c98f4e51 100644
--- a/services/analysis-engine/src/bandscope_analysis/youtube.py
+++ b/services/analysis-engine/src/bandscope_analysis/youtube.py
@@ -15,6 +15,7 @@
 import yt_dlp  # type: ignore
 
 YOUTUBE_VIDEO_ID_PATTERN = re.compile(r"^[A-Za-z0-9_-]{11}$")
+MAX_YOUTUBE_URL_LENGTH = 2000
 SUPPORTED_AUDIO_EXTENSIONS = (".opus", ".m4a", ".mp3", ".wav", ".aac", ".flac", ".ogg")
 YOUTUBE_DOWNLOAD_FAILED_MESSAGE = (
     "Failed to download audio from YouTube. Please use a local audio file instead."
@@ -32,6 +33,10 @@ def validate_url(url: str) -> bool:
     Returns:
         True if the URL is valid, False otherwise.
     """
+    # Pragmatic upper bound to avoid spending parser/downloader work on oversized user input.
+    if len(url) > MAX_YOUTUBE_URL_LENGTH:
+        return False
+
     try:
         parsed = urllib.parse.urlparse(url)
         if parsed.scheme != "https":
diff --git a/services/analysis-engine/tests/test_youtube.py b/services/analysis-engine/tests/test_youtube.py
index 71d7d60d..5531ac9d 100644
--- a/services/analysis-engine/tests/test_youtube.py
+++ b/services/analysis-engine/tests/test_youtube.py
@@ -7,7 +7,7 @@
 import pytest
 import yt_dlp  # type: ignore
 
-from bandscope_analysis.youtube import download_youtube_audio, validate_url
+from bandscope_analysis.youtube import MAX_YOUTUBE_URL_LENGTH, download_youtube_audio, validate_url
 
 
 def test_validate_url() -> None:
@@ -16,7 +16,11 @@ def test_validate_url() -> None:
     assert validate_url("https://youtu.be/abc123DEF45") is True
     assert validate_url("https://www.youtube.com/watch?v=abc123DEF45") is True
     assert validate_url("https://www.youtube.com/watch?v=abc123DEF45&t=10") is True
+    url_prefix = "https://youtube.com/watch?v=abc123DEF45&x="
+    max_length_url = url_prefix + ("a" * (MAX_YOUTUBE_URL_LENGTH - len(url_prefix)))
+    long_query_url = max_length_url + "a"
 
+    assert validate_url(max_length_url) is True
     assert validate_url("https://m.youtube.com/watch?v=abc123DEF45") is False
     assert validate_url("https://music.youtube.com/watch?v=abc123DEF45") is False
     assert validate_url("https://evil.youtube.com/watch?v=abc123DEF45") is False
@@ -34,6 +38,7 @@ def test_validate_url() -> None:
     assert validate_url("https://youtube.com/watch?v=abc123DEF45&v=") is False
     assert validate_url("https://youtube.com/watch?v=../../../etc/passwd") is False
     assert validate_url("https://youtu.be/../../../etc/passwd") is False
+    assert validate_url(long_query_url) is False
 
 
 def test_validate_url_edge_cases() -> None: