diff --git a/js/src/download.ts b/js/src/download.ts
index 578a811..8d6a89d 100644
--- a/js/src/download.ts
+++ b/js/src/download.ts
@@ -93,7 +93,7 @@ export async function ensureBinary(
         `CLOAKBROWSER_BINARY_PATH set to '${localOverride}' but file does not exist`
       );
     }
-    console.log(`[cloakbrowser] Using local binary override: ${localOverride}`);
+    console.error(`[cloakbrowser] Using local binary override: ${localOverride}`);
     return localOverride;
   }
 
@@ -159,7 +159,7 @@ export async function ensureBinary(
       return binaryPath;
     }
 
-    console.log(
+    console.error(
       `[cloakbrowser] Stealth Chromium ${requestedVersion} not found. Downloading for ${getPlatformTag()}...`
     );
     await downloadAndExtract(requestedVersion);
@@ -196,7 +196,7 @@ export async function ensureBinary(
   }
 
   // Download platform's hardcoded version
-  console.log(
+  console.error(
     `[cloakbrowser] Stealth Chromium ${platformVersion} not found. Downloading for ${getPlatformTag()}...`
   );
   await downloadAndExtract();
@@ -219,7 +219,7 @@ export function clearCache(): void {
   const cacheDir = getCacheDir();
   if (fs.existsSync(cacheDir)) {
     fs.rmSync(cacheDir, { recursive: true, force: true });
-    console.log(`[cloakbrowser] Cache cleared: ${cacheDir}`);
+    console.error(`[cloakbrowser] Cache cleared: ${cacheDir}`);
   }
 }
 
@@ -270,7 +270,7 @@ export async function checkForUpdate(): Promise<string | null> {
     return latest;
   }
 
-  console.log(`[cloakbrowser] Downloading Chromium ${latest}...`);
+  console.error(`[cloakbrowser] Downloading Chromium ${latest}...`);
   await downloadAndExtract(latest);
   writeVersionMarker(latest);
   return latest;
@@ -296,7 +296,7 @@ export async function checkForProUpdate(
   }
 
   if (!proBinaryReady(latest)) {
-    console.log(`[cloakbrowser] Downloading Pro Chromium ${latest}...`);
+    console.error(`[cloakbrowser] Downloading Pro Chromium ${latest}...`);
     await downloadProBinary(latest, licenseKey);
     if (!fs.existsSync(getBinaryPath(latest, true))) {
       throw new Error(
@@ -611,7 +611,7 @@ export function verifySignature(manifestBytes: Uint8Array, sigB64Bytes: Uint8Arr
     }
     try {
       if (cryptoVerify(null, manifestBytes, keyObject, signature)) {
-        console.log("[cloakbrowser] SHA256SUMS signature verified: Ed25519 OK");
+        console.error("[cloakbrowser] SHA256SUMS signature verified: Ed25519 OK");
         return;
       }
     } catch {
@@ -684,11 +684,11 @@ async function verifyChecksum(filePath: string, expectedHash: string): Promise<v
       `Please retry or report at https://github.com/CloakHQ/cloakbrowser/issues`
     );
   }
-  console.log("[cloakbrowser] Checksum verified: SHA-256 OK");
+  console.error("[cloakbrowser] Checksum verified: SHA-256 OK");
 }
 
 async function downloadFile(url: string, dest: string, headers?: Record<string, string>): Promise<void> {
-  console.log(`[cloakbrowser] Downloading from ${url}`);
+  console.error(`[cloakbrowser] Downloading from ${url}`);
 
   const controller = new AbortController();
   const timeout = setTimeout(() => controller.abort(), DOWNLOAD_TIMEOUT_MS);
@@ -731,7 +731,7 @@ async function downloadFile(url: string, dest: string, headers?: Record<string,
           lastLoggedPct = pct;
           const dlMB = Math.floor(downloaded / (1024 * 1024));
           const totalMB = Math.floor(total / (1024 * 1024));
-          console.log(
+          console.error(
             `[cloakbrowser] Download progress: ${pct}% (${dlMB}/${totalMB} MB)`
           );
         }
@@ -746,7 +746,7 @@ async function downloadFile(url: string, dest: string, headers?: Record<string,
     });
 
     const sizeMB = Math.floor(fs.statSync(dest).size / (1024 * 1024));
-    console.log(`[cloakbrowser] Download complete: ${sizeMB} MB`);
+    console.error(`[cloakbrowser] Download complete: ${sizeMB} MB`);
   } catch (err) {
     // Ensure file stream is destroyed on error to release the handle
     if (!fileStream.destroyed) {
@@ -808,7 +808,7 @@ async function ensureProBinary(
       showWelcome(welcomeTier);
       return getBinaryPath(requestedVersion, true);
     }
-    console.log(
+    console.error(
       `[cloakbrowser] Downloading Pro Chromium ${requestedVersion} for ${getPlatformTag()}...`
     );
     await downloadProBinary(requestedVersion, licenseKey);
@@ -884,7 +884,7 @@ async function ensureProBinary(
   // `version` (the server latest) needs downloading. On failure, fall back to a
   // cached Pro build if we have one — never the free binary.
   try {
-    console.log(
+    console.error(
       `[cloakbrowser] Downloading Pro Chromium ${version} for ${getPlatformTag()}...`
     );
     await downloadProBinary(version, licenseKey);
@@ -893,7 +893,7 @@ async function ensureProBinary(
     // cached-Pro fallback, which is only for transient download failures.
     if (err instanceof BinaryVerificationError) throw err;
     if (proBinaryReady(effective)) {
-      console.log(
+      console.error(
         `[cloakbrowser] Pro update to ${version} failed; launching cached Pro binary ${effective}`
       );
       showWelcome(welcomeTier);
@@ -1036,7 +1036,7 @@ async function extractArchive(
   destDir: string,
   binaryPath?: string
 ): Promise<void> {
-  console.log(`[cloakbrowser] Extracting to ${destDir}`);
+  console.error(`[cloakbrowser] Extracting to ${destDir}`);
   const bp = binaryPath || getBinaryPath();
 
   // Extract into a private sibling dir, then rename it into place. Concurrent
@@ -1100,7 +1100,7 @@ async function extractArchive(
   }
 
   if (fs.existsSync(bp)) {
-    console.log(`[cloakbrowser] Binary ready: ${bp}`);
+    console.error(`[cloakbrowser] Binary ready: ${bp}`);
   }
 }
 
@@ -1299,12 +1299,12 @@ async function checkAndDownloadUpdate(): Promise<void> {
       return;
     }
 
-    console.log(
+    console.error(
       `[cloakbrowser] Newer Chromium available: ${latest} (current: ${platformVersion}). Downloading in background...`
     );
     await downloadAndExtract(latest);
     writeVersionMarker(latest);
-    console.log(
+    console.error(
       `[cloakbrowser] Background update complete: Chromium ${latest} ready. Will use on next launch.`
     );
   } catch (err) {
diff --git a/js/src/geoip.ts b/js/src/geoip.ts
index 78dbd3e..0a13d0f 100644
--- a/js/src/geoip.ts
+++ b/js/src/geoip.ts
@@ -369,7 +369,7 @@ async function ensureGeoipDb(): Promise<string | null> {
 async function downloadGeoipDb(dest: string): Promise<void> {
   const dir = path.dirname(dest);
   fs.mkdirSync(dir, { recursive: true });
-  console.log("[cloakbrowser] Downloading GeoIP database (~70 MB)…");
+  console.error("[cloakbrowser] Downloading GeoIP database (~70 MB)…");
 
   const tmpPath = `${dest}.tmp.${Date.now()}`;
   try {
@@ -395,7 +395,7 @@ async function downloadGeoipDb(dest: string): Promise<void> {
     });
 
     fs.renameSync(tmpPath, dest);
-    console.log(`[cloakbrowser] GeoIP database ready: ${dest}`);
+    console.error(`[cloakbrowser] GeoIP database ready: ${dest}`);
   } catch (err) {
     if (fs.existsSync(tmpPath)) fs.unlinkSync(tmpPath);
     throw err;
diff --git a/js/tests/geoip.test.ts b/js/tests/geoip.test.ts
index 780a490..c5b6b45 100644
--- a/js/tests/geoip.test.ts
+++ b/js/tests/geoip.test.ts
@@ -127,6 +127,32 @@ describe("maybeResolveGeoip", () => {
     expect(fetchSpy.mock.calls[0][1]).toEqual({ redirect: "follow" });
   });
 
+  it("GeoIP database download writes nothing to stdout", async () => {
+    const cacheDir = fs.mkdtempSync(path.join(os.tmpdir(), "cloak-geoip-stdout-"));
+    tempDirs.push(cacheDir);
+    process.env.CLOAKBROWSER_CACHE_DIR = cacheDir;
+    process.env.CLOAKBROWSER_GEOIP_TIMEOUT_SECONDS = "0.001";
+
+    vi.spyOn(globalThis, "fetch").mockResolvedValue({
+      ok: true,
+      body: new ReadableStream({
+        start(controller) {
+          controller.enqueue(new Uint8Array([1, 2, 3]));
+          controller.close();
+        },
+      }),
+    } as Response);
+    vi.spyOn(console, "error").mockImplementation(() => {});
+    const consoleLog = vi.spyOn(console, "log").mockImplementation(() => {});
+    const stdoutWrite = vi.spyOn(process.stdout, "write");
+
+    await expect(resolveProxyGeo("http://203.0.113.10:8080")).rejects.toThrow();
+
+    expect(fs.existsSync(path.join(cacheDir, "geoip", "GeoLite2-City.mmdb"))).toBe(true);
+    expect(consoleLog).not.toHaveBeenCalled();
+    expect(stdoutWrite).not.toHaveBeenCalled();
+  });
+
   it("throws when the GeoIP database is unavailable", async () => {
     const cacheDir = fs.mkdtempSync(path.join(os.tmpdir(), "cloak-geoip-db-failure-"));
     tempDirs.push(cacheDir);
diff --git a/js/tests/update.test.ts b/js/tests/update.test.ts
index 8723031..4e8fd58 100644
--- a/js/tests/update.test.ts
+++ b/js/tests/update.test.ts
@@ -770,7 +770,7 @@ describe("concurrent first-run download", () => {
     "replaces a partial install left by an interrupted extraction",
     async () => {
       vi.spyOn(globalThis, "fetch").mockImplementation(async () => new Response(archiveBytes));
-      vi.spyOn(console, "log").mockImplementation(() => {});
+      vi.spyOn(console, "error").mockImplementation(() => {});
       fs.mkdirSync(path.join(getBinaryDir(), "lib"), { recursive: true });
       fs.writeFileSync(path.join(getBinaryDir(), "lib", "part-0.bin"), "truncated");
 
@@ -779,6 +779,22 @@ describe("concurrent first-run download", () => {
     },
   );
 
+  // MCP stdio servers use stdout as their JSON-RPC channel; status lines there break them.
+  it.skipIf(process.platform === "win32")(
+    "first-run download writes nothing to stdout",
+    async () => {
+      vi.spyOn(globalThis, "fetch").mockImplementation(async () => new Response(archiveBytes));
+      vi.spyOn(console, "error").mockImplementation(() => {});
+      const consoleLog = vi.spyOn(console, "log").mockImplementation(() => {});
+      const stdoutWrite = vi.spyOn(process.stdout, "write");
+
+      expect(await ensureBinary()).toBe(getBinaryPath());
+      expect(inspectInstall()).toBe("complete");
+      expect(consoleLog).not.toHaveBeenCalled();
+      expect(stdoutWrite).not.toHaveBeenCalled();
+    },
+  );
+
   it.skipIf(process.platform === "win32")(
     "concurrent processes replace a partial install left by an interrupted extraction",
     async () => {