Re:Show HN: ToolGuard – Pytest for AI agent tool calls
by Heer_J on Tuesday March 17, 2026 @09:25PM
(#47420591)
Totally spot on, Caleb! That was exactly the frustrating realization that led me to build this.
I've spend so much time obsessing over which model is smarter or tweaking our system prompts, but if a simple None value causes a backend TypeError that crashes the whole runtime, none of that reasoning truly matters. The agent is basically dead in the water.
By fuzzing the execution environment deterministically first, we can guarantee the "hands" of the agent work perfectly before we even bother testing the "brain". Plus, it runs in milliseconds during CI/CD instead of waiting for expensive API calls.
I've spend so much time obsessing over which model is smarter or tweaking our system prompts, but if a simple None value causes a backend TypeError that crashes the whole runtime, none of that reasoning truly matters. The agent is basically dead in the water.
By fuzzing the execution environment deterministically first, we can guarantee the "hands" of the agent work perfectly before we even bother testing the "brain". Plus, it runs in milliseconds during CI/CD instead of waiting for expensive API calls.