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Persona testing with browser use — having AI use a product as a specific persona like a PM coming out of a meeting — can reveal structural friction that synthetic user research misses.

Claire's husband EJ proposed having AI evaluate ChatPRD by role-playing specific users — a PM fresh from a meeting, an engineer picking up a PRD — which exposed a cross-thread reference flow problem Claire knew existed but had never experienced so acutely from the user's perspective. ✦ AI generated

Claire · Lenny's Newsletter · 2026-07-27 · original ↗

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Claire's husband, EJ, came up with the idea. Rather than asking AI to evaluate a product in the abstract, he suggested having it use the product as a specific person: a PM coming out of a meeting, an engineer picking up a PRD, or a team lead checking usage. In ChatPRD, this approach exposed a structural problem in the cross-thread reference flow. Claire already knew the issue existed, but she had never experienced it so clearly from the user's perspective.

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✳ ChatPRD ◉ EJ

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In practice · 1

EJ Lawless's persona-impersonation trick allows Codex to simulate different user perspectives, surfacing friction points the builder cannot see.Claire Vo · Lenny's Newsletter · conf 80%

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gives example → AI testing can be far more exhaustive than human testing because AI does not default to following the happy path, as demonstrated when Codex immediately found a blocking bug in an onboarding flow that had survived for months.Claire · Lenny's Newsletter gives example → Frontier models perform better and produce broader coverage when given room to decide how to approach a task rather than being handed a detailed checklist of steps.Claire · Lenny's Newsletter