Composing APIs and CLIs in the LLM era

We also use CLI tools for agents because it is obvious that they are good at it.

Our approach is slightly more complex because we need to supported fully authenticated sessions for end users and for shared credentials. It works by creating scoped API tokens to our service which get bundled into dynamically generated CLI clients. We point the agent to the client and voila. The agent can now run `some-command list-gmail-messages --query "tom"`. The oauth complexities, credential lifecycle and everything is handled automatically by the platform on the fly - it does not matter if the user is on Slack or access the agent through some chat interface or if the agent runs in the background doing work. It just works!

I've been beating this drum for the last 8 months.

The next frontier is using hooks to guide agents to use tools better and avoid doom loops.

This is what I’ve been doing too. Give the LLM a link to an OAS for an API and let it use curl for everything after that. I don’t even wrap the API or use restish all, the LLM knows how to use curl well enough.

This lets me add quick skills that are essentially just: “this is the OAS link, this is how you store and use the authorization, this is when I want you to use it”. That combined with pointing it at the documentation for common workflows and usage examples, and it’s been great.

The only thing I’ve had trouble with is auth really. MCPs are treated as first class citizens by most model provider’s agents and trying to provide a shell-based alternative for hiding the secret credentials from the LLM has been difficult.

Of all the interface modalities available, CLIs seem like the most natural for copilots to work with. Lots of examples in the training data, universal interface for help, maps well to the sequential nature of token generation, similar syntax for different OSs… I can see them replacing skills and MCP et al from the model’s perspective.

this seems like what MCPs should have been from the beginning. If you think MCPs are better, can you explain why?

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