Tessl is an AI developer platform and agent orchestration harness built to develop, evaluate, and optimize agent skills and coding workflows. It provides a structured CLI environment for managing repository skills, generating test scenarios, and systematically benchmarking agent performance against standardized developer tasks. In daily use, Tessl operates through the `tessl` CLI and integrates directly with agent runtimes such as Claude Code. Users can install skill packages, run static reviews of instruction files (`SKILL.md`), automatically generate multi-scenario evaluation suites, and execute differential evaluations with and without the skill active using models like Claude 3.7 Sonnet, Opus, or Haiku. Unlike traditional CLI agents that focus solely on executing single-turn code generation tasks, Tessl functions as an agent evaluation harness. It tests whether an agent correctly routes to a skill via activation evals, scores output deltas using LLM-as-a-judge rubrics, and categorizes findings into a four-bucket framework to pinpoint performance gaps, redundant context, and instruction-induced regressions.
Tags: ai agent, cli, code assistant, coding agent, developer tools, Generative AI