MCP customUserVars broken when MCP server name has spaces/punctuation in it

[notfoundry]

What happened?

When creating a MCP tool, the LangChain tool name is computed as `${toolName}${Constants.mcp_delimiter}${normalizeServerName(serverName)}`. The normalizeServerName() function strips out various special characters and replaces them with underscores; for example, a server in librechat.yaml named "Connector: Microsoft" would be normalized as "Connector__Microsoft". However, this seems to be the only place in Librechat that normalizes the MCP server name. The tools cache uses unmodified name, and inside getUserMCPAuthMap(), the server's name (used for looking up the saved credentials) is computed as ${Constants.mcp_prefix}${serverName}. Since the normalized server name for the tool was inconsistent with how it was stored, Librechat will never be able to find the credentials for those MCP servers, and tool calling with user-provided credentials will be broken.

I'm assuming this is a real bug, since nowhere in the Librechat documentation does it say that having spaces in user-selectable MCP servers isn't permitted, and every other aspect of MCP tool calling works flawlessly. I found that making the following substitution in getUserMCPAuthMap() addressed the issue. I'm just leaving on vacation so don't have time to make a MR this second, but maybe it will be useful:

     const toolKey = tool.name;
-    if (toolKey && appTools[toolKey] && mcpToolPattern.test(toolKey)) {
-      const parts = toolKey.split(Constants.mcp_delimiter);
-      const serverName = parts[parts.length - 1];
-      uniqueMcpServers.add(`${Constants.mcp_prefix}${serverName}`);
+    if (toolKey && mcpToolPattern.test(toolKey)) {
+      const originalToolKey = appTools[toolKey]
+        ? toolKey
+        : Object.keys(appTools).find(key => normalizeServerName(key) === toolKey);
+
+      if (originalToolKey) {
+        const parts = originalToolKey.split(Constants.mcp_delimiter);
+        const serverName = parts[parts.length - 1];
+        uniqueMcpServers.add(`${Constants.mcp_prefix}${serverName}`);
+      }
     }

Version Information

Commit 62c3f13

Steps to Reproduce

See description.

What browsers are you seeing the problem on?

No response

Relevant log output

N/A. No log output indicating an error exists. Substituting in credentials silently fails.

Screenshots

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[danny-avila]

@dustinhealy can you look into this?

the only aspect about this being a potential bug is the tool not resolving with the unmodified name.

the normalization is done as some providers will not support special characters in the function name.

also @notfoundry if you’re in control of the MCP server, you can avoid this problem by renaming the function names. Certain LLM providers will throw an error when they’re used anyway.

if using a public MCP server, please share so we can troubleshoot.

[notfoundry]

Any / all MCP servers should be affected, since (if I understood correctly why the fix worked) the controlling input is just whatever the server's key/name is in librechat.yaml. I'll see if I can find a minimal server + tool that'll visibly display the problem, I think all that any server would see is {{ YOUR_VAR }} in the env / headers instead of the substituted value of YOUR_VAR

[danny-avila]

that's right, the server name is what's actually normalized, and can be defined in the yaml, so you can avoid this issue directly by changing it in the definition under mcpServers:

[danny-avila]

we're working on a possible solution here, so it can be handled whether or not there are special chars. in the name

[danny-avila]

Closed by #8644