Codebase Onboarding Agent

A GitLab Duo custom agent that turns any repository into an instant onboarding guide. Type "onboard me" and get a full codebase walkthrough, health score, and personal checklist issue, in 30 seconds.

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Inspiration

New developers waste weeks trying to understand an unfamiliar codebase. They read outdated wikis, interrupt senior developers with basic questions, and piece together architecture from scattered comments. Studies show developers take 3 months to a full year to reach full productivity on a new codebase. We built the Codebase Onboarding Agent to fix this.

What it does

A custom GitLab Duo agent that turns any repository into an instant onboarding experience. Type "onboard me" and the agent reads your entire codebase, directory structure, key files, recent commits, open issues, then generates a personalized guide with tech stack, architecture explanation, learning path, and gotchas. It also creates a personal checklist issue with checkbox learning steps assigned to you. Type "\health" to get a scored health report across 5 dimensions with a concrete action plan.

How we built it

Built entirely on GitLab Duo Agent Platform using 16 tools including List Repository Tree, Read Files, Grep, Get Project, List Commits, and Create Issue. The intelligence lives in a carefully engineered system prompt, no backend servers, no infrastructure to maintain.

Challenges we ran into

Designing a system prompt that forces structured output without breaking on unusual codebases. Selecting the right tool combination, too few misses context, too many unfocuses responses. Calibrating health scores meaningfully across repos of different sizes and languages.

Accomplishments that we're proud of

  • Works on ANY GitLab repository regardless of language or framework
  • Zero infrastructure required, entire intelligence lives in the system prompt
  • Creates real GitLab artifacts, checklist issues with trackable checkboxes
  • \health command produces genuinely actionable improvement plans

What we learned

GitLab Duo Agent Platform is remarkably powerful for building domain-specific agents. The tool selection and system prompt engineering are the core skills. Claude AI's reasoning capabilities make it possible to draw real insights from raw repository data.

What's next for Codebase Onboarding Agent

  1. Automated Flow trigger when new member joins a project
  2. Role-based learning paths (frontend vs backend vs devops)
  3. Weekly "what changed" digest command
  4. Multi-language onboarding path detection
  5. Integration with GitLab onboarding issue templates

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