Tag: mcp

Claude Code logs every MCP server stderr line at [ERROR] and marks working servers as failed. If your tools still run, it is cosmetic. Here is how to confirm it and quiet the noise.

One trailing comma or unescaped Windows path in your MCP config makes every server vanish, not just the broken one. Validate the JSON, fix the five usual suspects, restart.

Commit .cursor/mcp.json for the IDE, register shared servers under Dashboard > Integrations & MCP for cloud agents, and keep secrets out of git with ${env:...}. The full two-surface setup for Cursor 3.11 (July 2026), including why the repo file alone does not reach cloud agents.

A step-by-step checklist for lifting a hand-rolled Anthropic tool-calling loop onto a standalone MCP server. The tool bodies move almost verbatim; what changes is where the schema comes from, how results are wrapped, and how errors cross the process boundary.

A step-by-step checklist for moving an existing LangChain agent off inline @tool functions onto a standalone MCP server that any client can call. Covers extracting tools into FastMCP, re-wiring the agent with langchain-mcp-adapters MultiServerMCPClient, the sync-to-async switch, transports, and the gotchas that bite mid-cutover.

Build a skill to change how Claude works, a subagent to protect your context window, and an MCP server to reach a system Claude cannot otherwise touch. They solve three different problems, not one. Here is the decision, the mechanics, and the config for each.

Use CodeAct (the agent writes executable code as its action) when your tasks chain many tools, loop, or move large data, and you can afford a sandbox. Use the JSON tool-calling loop for a handful of discrete, high-stakes actions where a code interpreter is overkill or unsafe. CodeAct wins on token cost and multi-step success rate; tool calling wins on safety and simplicity.

MCP connects one agent to its tools, A2A connects independent agents to each other. They are not competitors. Add MCP first, reach for A2A only when you have multiple separately deployed agents. Here is the wire-level difference and the code.

Cato AI Labs disclosed CVE-2026-50548 and CVE-2026-50549, a pair of 9.8 CVSS flaws in Cursor's terminal sandbox. A poisoned MCP response or web result can escape the sandbox and run code. Cursor 3.0 is the fix.

Use stdio for a local server one client launches, use Streamable HTTP for anything remote or multi-client, and do not build new HTTP+SSE servers -- that transport was deprecated in the 2025-03-26 MCP spec. Here is the decision, the wire-level differences, and the code for each.