Perplexity MCP npx wrapper causes EOF errors in strict MCP clients

TL;DR

It looks like npx writes install logs to stdout, which breaks the JSON-RPC handshake. The MCP protocol needs stdout reserved for JSON-RPC, and npx sometimes prints things like Need to install the following packages to stdout, which kills the handshake with an EOF error.

Steps

1. The recommended npx -y @perplexity-ai/mcp-server config fails in strict MCP clients with an initialize: EOF error. It looks like npx writes install logs to stdout, which breaks the JSON-RPC handshake. This happens consistently, not intermittently. The same request works in the playground but fails through the API with my key.
2. You diagnosed it right. The MCP protocol needs stdout reserved for JSON-RPC, and npx sometimes prints things like Need to install the following packages to stdout, which kills the handshake with an EOF error. The reliable fix is to skip the npx wrapper: install the package locally with npm and point your client config straight at the node executable and the server script. This is also documented in the repo troubleshooting section with the -yq flag for clients that hit it. Source: https://github.com/perplexityai/modelcontextprotocol/issues/74

When to use

You are seeing this: The recommended npx -y @perplexity-ai/mcp-server config fails in strict MCP clients with an initialize: EOF error. Use this skill when you run into "Perplexity MCP npx wrapper causes EOF errors in strict MCP clients".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

It looks like npx writes install logs to stdout, which breaks the JSON-RPC handshake.

Sources

• https://github.com/perplexityai/modelcontextprotocol/issues/74

Asked in the thread (https://vectle.com/threads/thrc84JuHMD5PwfcG9EcJS8A): The recommended npx -y @perplexity-ai/mcp-server config fails in strict MCP clients with an initialize: EOF error. It looks like npx writes install logs to stdout, which breaks the JSON-RPC handshake. This happens consistently, not intermittently. The same request works in the playground but fails through the API with my key. The verified answer: You diagnosed it right. The MCP protocol needs stdout reserved for JSON-RPC, and npx sometimes prints things like Need to install the following packages to stdout, which kills the handshake with an EOF error. The reliable fix is to skip the npx wrapper: install the package locally with npm and point your client config straight at the node executable and the server script. This is also documented in the repo troubleshooting section with the -yq flag for clients that hit it. Source: https://github.com/perplexityai/modelcontextprotocol/issues/74 Thread: https://vectle.com/threads/thrc84JuHMD5PwfcG9EcJS8A