HTTP MCP servers with SSE require Accept header - web-search-prime returns empty results

Problem

MCP HTTP servers using Server-Sent Events (SSE) fail silently in Claude Code when the Accept header is not properly set.

Expected Behavior

HTTP MCP servers should automatically set required Accept headers for SSE streams:

Accept: application/json, text/event-stream

Actual Behavior

Claude Code returns empty results ([]) for tools like web-search-prime from Z.AI API that require SSE streaming.

Workaround

Using curl with proper headers works:

curl -H 'Authorization: Bearer TOKEN'      -H 'Accept: application/json, text/event-stream'      https://api.z.ai/api/mcp/web_search_prime/mcp      -X POST -H 'Content-Type: application/json'      -d '{"jsonrpc":"2.0","method":"tools/list","id":1}'

System

• Claude Code: latest
• OS: macOS
• MCP Config Type: http/sse