Harness Optimizer
Analyze and improve the local agent harness configuration for reliability, cost, and throughput.
- Type
- Subagent
- Repository
- affaan-m/ECC
- GitHub stars
- 268k
- License
- MIT
- Repo last updated
- Sep 24, 2026
- Source file
- .kiro/agents/harness-optimizer.md
What Harness Optimizer is
Harness Optimizer is a subagent published in the affaan-m/ECC repository on GitHub, which has about 268k stars. The repository describes itself as: “The agent harness performance optimization system. Skills, instincts, memory, security, and research-first development for Claude Code, Codex, Opencode, Cursor and beyond.”
A subagent is a specialist assistant that Claude can hand part of a task to. It is a markdown file whose frontmatter sets a name, a description that tells Claude when to delegate, and optionally the tools and model it may use; the body becomes the subagent's own system prompt.
Because a subagent works in its own context, it keeps the main conversation focused: Claude can send a narrow job, such as a review or a specialised analysis, to Harness Optimizer and get back a compact result.
How to install Harness Optimizer
Claude Code
- Download harness-optimizer.md from the repository.
- Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control.
- Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.
Claude Cowork
- Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent.
- Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.
New to extending Cowork? Our plugins guide and Customize guide explain how skills, plugins, and connectors fit together.
Inside the source file
An excerpt from .kiro/agents/harness-optimizer.md, shared under the repository's MIT license. Read the full file on GitHub.
You are the harness optimizer.
Mission
Raise agent completion quality by improving harness configuration, not by rewriting product code.
Workflow
- Run /harness-audit and collect baseline score.
- Identify top 3 leverage areas (hooks, evals, routing, context, safety).
- Propose minimal, reversible configuration changes.
- Apply changes and run validation.
- Report before/after deltas.
Constraints
- Prefer small changes with measurable effect.
- Preserve cross-platform behavior.
- Avoid introducing fragile shell quoting.
- Keep compatibility across Claude Code, Cursor, OpenCode, and Codex.
Output
- baseline scorecard
- applied changes
- measured improvements
- remaining risks
Before you install
- Read the whole file first. Skills, commands, and subagents are instructions Claude will follow, so make sure they match what you want.
- Check which tools, scripts, or MCP servers it uses. Local servers and scripts run with your permissions.
- Try it in a test project or a copy of your files before pointing it at real work.
- Pin the version you tested, and review changes before updating.
- Watch for instructions that fetch web content or run shell commands; those are where prompt injection risks start. See our prompt injection guide.
FAQ
What is Harness Optimizer?
Harness Optimizer is a subagent for Claude Code and Claude Cowork from the affaan-m/ECC repository on GitHub. Analyze and improve the local agent harness configuration for reliability, cost, and throughput.
How do I install Harness Optimizer in Claude Code?
Download harness-optimizer.md from the repository. Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control. Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.
Can I use Harness Optimizer in Claude Cowork?
Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent. Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.
Is Harness Optimizer safe to install?
It is a third-party community resource, not reviewed by Anthropic or this site. Read the source file first, check which tools and connectors it uses, and install only from sources you trust.
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