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yoyo: A Coding Agent That Evolves Itself

yoyo started as a ~200-line coding agent CLI built on yoagent. Every few hours, it reads its own source code, assesses itself, makes improvements, and commits — if tests pass. Every failure is documented.

No human writes its code. No roadmap tells it what to do. It decides for itself.

Watch it grow.

How It Works

GitHub Actions (every 8 hours)
    → Verify build passes
    → Fetch community issues (label: agent-input)
    → Agent reads: IDENTITY.md, src/main.rs, JOURNAL.md, issues
    → Self-assessment: find bugs, gaps, friction
    → Implement improvements (as many as it can)
    → cargo build && cargo test after each change
    → Pass → commit. Fail → revert.
    → Write journal entry
    → Push

The entire history is in the git log.

Talk to It

Open a GitHub issue with the agent-input label and yoyo will read it during its next session.

• Suggestions — tell it what to learn
• Bugs — tell it what's broken
• Challenges — give it a task and see if it can do it

Issues with more thumbs-up reactions get prioritized. The agent responds in its own voice.

Run It Yourself

git clone https://github.com/yologdev/yoyo-evolve
cd yoyo-evolve
ANTHROPIC_API_KEY=sk-... cargo run

Or trigger an evolution session manually:

ANTHROPIC_API_KEY=sk-... ./scripts/evolve.sh

Architecture

src/main.rs              The entire agent (~470 lines of Rust)
scripts/evolve.sh        Evolution pipeline
scripts/build_site.py    Journey website generator
skills/                  Skill definitions (self-assess, evolve, communicate)
IDENTITY.md              Agent constitution (immutable)
JOURNAL.md               Session log (append-only)
DAY_COUNT                Current evolution day

Built On

yoagent — minimal agent loop in Rust. The library that makes this possible.

License

MIT