MCP Server Error Handling: What I Learned
I thought I was finished after my MCP server ran for the first time. It returned a tool list. It called a tool. I felt successful.
I was wrong.
Running an MCP server in production taught me that tutorials focus on the happy path. They ignore what happens when things break. Here is what I learned while building a server for my 1,800-hour knowledge base.
Always return content for empty results Most clients hang when they receive an empty response. If your search finds nothing, do not return nothing. Return a text message. Tell the user why there are no results and how many items exist in your database.
Manage slow connection starts I host on a free tier that sleeps. When it wakes up, it takes 15 seconds. Many MCP clients timeout before then. • Send early headers to keep the connection alive. • Set hard limits on response size. Truncate large results so you do not hit timeout limits.
Stop manual JSON building One unescaped double quote in a title broke my entire JSON response. The client disconnected without an error. Use a framework like Jackson to handle serialization. Let the library manage escaping for you.
Expect inconsistent authentication Different clients handle API keys differently. Some use headers. Some use query parameters. Some use neither. • Support multiple ways to send keys. • Always return a proper JSON error body if auth fails.
Set explicit Content-Length Some clients struggle with chunked encoding. If your responses truncate, stop using compression. Precompute your response size and set the Content-Length header explicitly.
The Pros: • Privacy: Only relevant snippets go to the AI. • Interoperability: The server works across different clients. • Simplicity: My server is only 150 lines of code.
The Cons: • Young ecosystem: Documentation is missing many edge cases. • Hosting: You must manage your own endpoints and cold starts. • Evolution: The protocol changes often.
MCP turned my unused notes into a useful tool. It makes my data available so the AI can do the heavy lifting.
Have you built an MCP server? What errors did you face? Let me know in the comments.
Optional learning community: https://t.me/GyaanSetuAi