From 3b9881c2dd2ea73a8b5c02bc558046121fa2dc61 Mon Sep 17 00:00:00 2001
From: haosenwang1018 <haosenwang1018@users.noreply.github.com>
Date: Sat, 18 Apr 2026 06:11:36 +0000
Subject: [PATCH] fix: only show server stderr in debug mode

Signed-off-by: haosenwang1018 <haosenwang1018@users.noreply.github.com>
---
 src/client.ts | 19 +++++++------------
 src/index.ts  |  6 ++++++
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/src/client.ts b/src/client.ts
index 50731cf..26f635c 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -244,14 +244,16 @@ export async function connectToServer(
       transport = createStdioTransport(config);
 
       // Capture stderr for debugging - attach BEFORE connect
-      // Always stream stderr immediately so auth prompts are visible
       const stderrStream = transport.stderr;
       if (stderrStream) {
         stderrStream.on('data', (chunk: Buffer) => {
           const text = chunk.toString();
           stderrChunks.push(text);
-          // Always stream stderr immediately so users can see auth prompts
-          process.stderr.write(`[${serverName}] ${text}`);
+
+          // Only forward live stderr in debug mode to avoid noisy token burn.
+          if (process.env.MCP_DEBUG) {
+            process.stderr.write(`[${serverName}] ${text}`);
+          }
         });
       }
     }
@@ -268,15 +270,8 @@ export async function connectToServer(
       throw error;
     }
 
-    // For successful connections, forward stderr to console
-    if (!isHttpServer(config)) {
-      const stderrStream = (transport as StdioClientTransport).stderr;
-      if (stderrStream) {
-        stderrStream.on('data', (chunk: Buffer) => {
-          process.stderr.write(chunk);
-        });
-      }
-    }
+    // For successful connections, stderr has already been captured above.
+    // It is only forwarded live when MCP_DEBUG is enabled.
 
     return {
       client,
diff --git a/src/index.ts b/src/index.ts
index 088deed..0414003 100755
--- a/src/index.ts
+++ b/src/index.ts
@@ -129,6 +129,10 @@ function parseArgs(args: string[]): ParsedArgs {
         result.command = 'version';
         return result;
 
+      case '--debug':
+        process.env.MCP_DEBUG = '1';
+        break;
+
       case '-d':
       case '--with-descriptions':
         result.withDescriptions = true;
@@ -367,6 +371,7 @@ Options:
   -v, --version            Show version number
   -d, --with-descriptions  Include tool descriptions
   -c, --config <path>      Path to mcp_servers.json config file
+  --debug                  Show MCP server stderr/debug output
 
 Output:
   mcp-cli/info/grep        Human-readable text to stdout
@@ -385,6 +390,7 @@ Examples:
 Environment Variables:
   MCP_NO_DAEMON=1        Disable connection caching (force fresh connections)
   MCP_DAEMON_TIMEOUT=N   Set daemon idle timeout in seconds (default: 60)
+  MCP_DEBUG=1            Show MCP server stderr/debug output
 
 Config File:
   The CLI looks for mcp_servers.json in: