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“You Said No MCP!”
Hraness wrote this summary from a saved copy of the source. Quotations are taken word for word from the source.
gist
Earendil Engineering explains why Pi added the Model Context Protocol (MCP): current MCP is better, and Codemode makes its tools composable inside a JavaScript sandbox. The post still calls composition the central weakness, arguing that servers should expose structured data with intelligent tool discovery, closer to OpenAPI. Pi's newer model support also required deferred tools and Codemode-only configuration. The authors present adoption as a way to shape MCP for small harnesses while its servers and patterns continue to improve.
ideas
- Pi moved MCP into its core after the supporting changes proved useful beyond MCP. The same interpreter sandbox also enables the use of Jev more easily within Pi.
- MCP's remaining weakness is composition. Earendil says many servers dump text-returning tools into context and argues for structured data plus documentation-based discovery, closer to OpenAPI.
- Codemode lets agents orchestrate tools inside the harness. Its JavaScript sandbox combines calls in the order the agent chooses, while keeping state in the session transcript.
- Modern model capabilities changed Pi's tool configuration needs. Deferred tool loading, mid-conversation system messages, and reasoning-level changes require tools to be deferred or Codemode-specific.
- Earendil is adopting MCP to shape its small-harness future. The post says servers and usage patterns still need improvement.
quotes
“The biggest issue with MCP continues to be that it’s hard to compose.”
“The way we like to think about MCP at this point is that it should be much closer to OpenAPI with intelligent tool discovery.”
“Codemode is special in that it runs where the harness runs.”
“We believe the best way to positively influence something is to embrace it.”