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Quoting Jeremy Daer

RSS January 17, 2026
Score: 8.7

Interest Score Breakdown

Seismic Impact (30%)

8.0/10

How newsworthy is this in AI?

Ecosystem Relevance (70%)

9.0/10

How useful for your apps?

Summary

[On agents using CLI tools in place of REST APIs] To save on context window, yes, but moreso to improve accuracy and success rate when multiple tool calls are involved, particularly when calls must be correctly chained e.g. for pagination, rate-limit backoff, and recognizing authentication failures.


Other major factor: which models can wield the skill? Using the CLI lowers the bar so cheap, fast models (gpt-5-nano, haiku-4.5) can reliably succeed. Using the raw APl is something only the costly "strong" models (gpt-5.2, opus-4.5) can manage, and it squeezes a ton of thinking/reasoning out of them, which means multiple turns/iterations, which means accumulating a ton of context, which means burning loads of expensive tokens. For one-off API requests and ad hoc usage driven by a developer, this is reasonable and even helpful, but for an autonomous agent doing repetitive work, it's a disaster.


Jeremy Daer, 37signals

Tags: prompt-engineering, skills, generative-ai, 37-signals, ai, llms

How to Use in Your Ecosystem

For Zac's ecosystem, this insight is directly applicable to the orchestrator's agent design, particularly in how Claude agents like rails-expert and test-engineer interact with CLI tools across multiple Rails apps. The strategy of using CLI for more reliable, lower-context tool chaining could significantly improve the orchestrator's ability to handle complex tasks like automated testing, code generation, and deployment across the diverse suite of infrastructure and game applications.

Source

https://simonwillison.net/2026/Jan/17/jeremy-daer/#atom-everything