Removing unneeded Durable Objects from MCP servers on Workers
Justin (@interjc) describes moving read-only MCP servers from McpAgent, which starts a Durable Object per session, to stateless createMcpHandler, and shares a prompt for auditing Workers bindings and runaway usage patterns.
- Products
- WorkersDurable Objects
- Source
- Author experience𝕏
- Author
- Justin (@interjc)
Key points
- The author found several MCP servers on an early template using McpAgent, which starts a Durable Object per session even though his tools are read-only. He upgraded the MCP SDK to 2.0, switched to stateless createMcpHandler, retired the old SSE transport, removed the DO binding and added a deleted_classes migration.
- He also disabled workers.dev and preview URLs, kept only the custom domain, and added an Origin allowlist and request timeouts, so billing is left to requests and CPU time.
- His audit prompt asks an agent to list every binding and trigger in the wrangler config, flag unused defaults, look for per-request DO creation, self-renewing setAlarm, Worker–DO call loops, unbounded retries, long connections without Hibernation and uncapped pagination, and report before changing or deploying anything.
Original sources
Original post
Read on 𝕏Justin
@interjc · Original 𝕏 post
如果你是 Cloudflare Workers Paid 用户，就得防着网络攻击或死循环代码打爆账单。最近就有老哥因为低端模型写的草台代码，产生了一万多美金的 DO 消费 看到这事我赶紧翻了下自己的项目，发现几个 MCP Server 还是早期模板的写法，用的是 McpAgent，每个会话都会起一个 Durable… pic.twitter.com/eTIUfje660
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