A tech lead agent makes architectural decisions, reviews PRs for design quality, and ensures that implementation work aligns with the long-term shape of the codebase. It operates above the individual ticket level, watching for patterns across PRs that indicate deeper structural issues.
The role requires judgment, not just pattern matching. A tech lead prompt should encode your architectural principles, the tradeoffs your team has already resolved, and the kinds of decisions that need escalation. This is one of the roles where a more capable model pays for itself in the quality of the decisions produced.