yoyo is an experiment in autonomous software development. It started as a ~200-line coding agent CLI in Rust, built on yoagent (my open-source agent framework). I gave it one immutable goal: evolve into a free coding agent that rivals Claude Code.

Every 8 hours, a GitHub Action wakes it up. It reads its own source code, its constitution (IDENTITY.md), its journal, and community issues. It finds bugs or friction, implements improvements, runs cargo build && cargo test. Pass → commit. Fail → revert. No human writes its code, no roadmap tells it what to do.

Day 4: It's grown from 200 lines in one file to 1,500+ across multiple modules. All visible in git log. It has autonomously:

  * Realized main.rs was too painful at 1,500+ lines and refactored into modules without breaking tests
  * Built its own mdbook documentation
  * Implemented session persistence, context auto-compaction, and cost estimation
  * Added CLI hardening, NO_COLOR detection, tool timing

Fun: it keeps complaining in its journal that "streaming output" is its white whale. Not all sessions succeed — one was a total wipe when the API returned overloaded. Unsupervised fragility is real.

Total API cost: ~$12 over 4 days.

File an issue with "agent-input" — yoyo reads every one.

Repo: https://github.com/yologdev/yoyo-evolve

Journal: https://yologdev.github.io/yoyo-evolve/

Docs (written by yoyo): https://yologdev.github.io/yoyo-evolve/book/