What a harness is and how to build one with Claude Agent SDK

Claire Vo built a custom AI harness for bug triage at ChatPRD using the Claude Agent SDK, a terminal UI with Ink, and adapters for Sentry, Linear, GitHub, and Vercel. The harness automates evidence gathering, root-cause analysis, and artifact creation, eliminating repetitive manual debugging. Vo explains the architecture and provides a guide for building similar harnesses for structured workflows.

Everybody is saying, “It’s not the model, it’s the harness,” but almost nobody stops to explain what a harness actually is. So I did. I built one live on the show: a Sentry bug-debugging harness for my company ChatPRD, using the Claude Agent SDK, a custom terminal UI built with the Ink library, and opinionated adapters for Sentry, Linear, GitHub, and Vercel. The harness handles evidence gathering, root-cause analysis, and follow-up artifact creation, all without me needing to type “dear agent, please fix this bug” ever again. I also walk through the architecture, share the code structure, and give you the exact process I used so you can build your own harness for any repetitive, structured workflow in your business. Listen or watch on YouTube, Spotify, or Apple Podcasts What you’ll learn: What a harness actually is When to build a harness versus when to stick with a general-purpose tool like Claude Code or Codex How to encode specific permissions into a harness The three components every harness needs How I used GPT-5.5 and Claude Opus to build the harness code itself and where they both initially resisted How to structure the artifacts your harness produces so the whole team can use the output Brought to you by: Bolt.new —Turn your idea into a real product Customer.io —Build customer engagement campaigns from a single prompt In this episode, we cover: 00:00 https://www.youtube.com/watch?v=ofS-4RRw9zw What is an AI harness? 03:19 https://www.youtube.com/watch?v=ofS-4RRw9zw&t=199s When to build a harness 04:33 https://www.youtube.com/watch?v=ofS-4RRw9zw&t=273s Why Claire picked bug triage 06:00 https://www.youtube.com/watch?v=ofS-4RRw9zw&t=360s Why not just use Claude Code? 07:48 https://www.youtube.com/watch?v=ofS-4RRw9zw&t=468s Demo: The custom harness interface 11:04 https://www.youtube.com/watch?v=ofS-4RRw9zw&t=664s Architecture: runs, tasks, tools, and artifacts 13:44 https://www.youtube.com/watch?v=ofS-4RRw9zw&t=824s Building it with Codex and Claude 15:08 https://www.youtube.com/watch?v=ofS-4RRw9zw&t=908s Code map and file layout 16:51 https://www.youtube.com/watch?v=ofS-4RRw9zw&t=1011s A look at the code 19:18 https://www.youtube.com/watch?v=ofS-4RRw9zw&t=1158s The live investigation result 21:01 https://www.youtube.com/watch?v=ofS-4RRw9zw&t=1261s How to build your own harness Tools referenced: • Claude Agent SDK Anthropic : https://code.claude.com/docs/en/agent-sdk/overview https://code.claude.com/docs/en/agent-sdk/overview • Claude Sonnet 4.6 model used inside the harness : https://www.anthropic.com/news/claude-sonnet-4-6 https://www.anthropic.com/news/claude-sonnet-4-6 • Claude Opus used to build the harness : https://www.anthropic.com/claude/opus https://www.anthropic.com/claude/opus • GPT-5.5 Codex, used to build the harness : https://openai.com/index/introducing-gpt-5-5/ https://openai.com/index/introducing-gpt-5-5/ • Ink terminal UI library for Node.js : https://github.com/vadimdemedes/ink https://github.com/vadimdemedes/ink • Sentry error monitoring : https://sentry.io/ https://sentry.io/ • Linear project management : https://linear.app/ https://linear.app/ • GitHub: https://github.com/ https://github.com/ • Vercel: https://vercel.com/ https://vercel.com/ Where to find Claire Vo: ChatPRD: https://www.chatprd.ai/ https://www.chatprd.ai/ Website: https://clairevo.com/ https://clairevo.com/ LinkedIn: https://www.linkedin.com/in/clairevo/ https://www.linkedin.com/in/clairevo/ Production and marketing by https://penname.co/ https://penname.co/ . For inquiries about sponsoring the podcast, email email protected /cdn-cgi/l/email-protection .