--- title: "The Repo Is the Harness — How we made an 8-year-old codebase agent-native" url: https://daily.dev/posts/the-repo-is-the-harness-how-we-made-an-8-year-old-codebase-agent-native-o9z6tqgjb source_url: https://blog.streamlit.io/the-repo-is-the-harness-how-we-made-an-8-year-old-codebase-agent-native-75629a953354 type: article source: "Streamlit" published: 2026-07-08T19:10:28.232Z updated: 2026-07-08T19:12:20.006Z tags: ["ai-agents", "claude-code", "spec-driven-development"] reading_time: 9 upvotes: 0 comments: 0 language: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # The Repo Is the Harness — How we made an 8-year-old codebase agent-native **[Streamlit](https://daily.dev/sources/streamlit)** · 9 min read · 0 upvotes · 0 comments ## Summary The Streamlit team shares how they redesigned their 8-year-old open-source Python codebase to work effectively with AI coding agents. Rather than relying on better prompts or models, they built a layered 'harness' system: simplifying the codebase to reduce agent confusion, tightening linting/type-checking guardrails across Python/TypeScript/Protobuf, moving all project knowledge (AGENTS.md files, architecture docs, specs) into the repo, packaging recurring work into reusable skills and subagents, adding multi-model AI PR review, and automating maintenance tasks via GitHub Actions. The result: features that took a sprint now ship in hours, newly reported bugs are at a three-year low, and agents handle the majority of feature work and maintenance while humans focus on product, architecture, and design decisions. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: --- Tags: [#ai-agents](https://daily.dev/tags/ai-agents), [#claude-code](https://daily.dev/tags/claude-code), [#spec-driven-development](https://daily.dev/tags/spec-driven-development) [View this post on daily.dev](https://daily.dev/posts/the-repo-is-the-harness-how-we-made-an-8-year-old-codebase-agent-native-o9z6tqgjb)