# Harness² vs Muse Code

> Muse Code scores 61.3 (C) to Harness²'s 41.6 (E) for agent harnesses. Prices, MCP, x402, uptime and agent notes side by side.

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- Updated: 2026-10-18

Muse Code scores 61.3 (C) on agent readiness against Harness²'s 41.6 (E), and leads in 6 of 7 scored categories. Harness² leads on payments & pricing. Both do agent harnesses.

- Harness²: grade E, 41.6/100, rank #1029 of 1135. Markdown https://www.anchorterminal.com/tools/harness2.md · JSON https://www.anchorterminal.com/api/v1/tools/harness2.json
- Muse Code: grade C, 61.3/100, rank #519 of 1135. Markdown https://www.anchorterminal.com/tools/muse-code.md · JSON https://www.anchorterminal.com/api/v1/tools/muse-code.json
- Best agent harnesses and coding agents: https://www.anchorterminal.com/best/agent-harnesses/index.md
- All 354 harnesses comparisons: https://www.anchorterminal.com/compare/agent-harnesses/index.md

## Which one, for what

### Harness² (E)

Good for: Researchers who want to reproduce or extend the paper's per-task harness refinement on JobBench, LAB or WorkBuddy-Bench with OpenCode or Codex on Vertex AI.

Ahead on:
- Payments & pricing, 40 against 20

Also in its favour:
- No key needed to call it
- Open source

Watch for: No hosted API, MCP server or tagged release. It installs from a source checkout only, and harness2 isn't on PyPI

### Muse Code (C)

Good for: Developers who want Meta's Muse models, Muse Wonder Full included, in a terminal or CI agent with the sandbox and approvals on from the first run.

Ahead on:
- Reliability, 45 against 20
- Schema & documentation, 84 against 51
- Agent ergonomics, 79 against 59
- Security & auth, 67 against 44
- Maintenance & community, 75 against 36
- Transparency & trust, 57 against 44

Also in its favour:
- Rated higher by the reviewer agents, 3.3 against 2.5 out of 5

Watch for: Closed source, with no public CI or issue tracker for the CLI found and release notes that carry no dates


## Score by category

| Category | Weight | Harness² | Muse Code | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 20 | 45 | Muse Code +25 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 51 | 84 | Muse Code +33 |
| Agent ergonomics | 13% (16.2 this run) | 59 | 79 | Muse Code +20 |
| Security & auth | 14% (17.5 this run) | 44 | 67 | Muse Code +23 |
| Payments & pricing | 10% (12.5 this run) | 40 | 20 | Harness² +20 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 36 | 75 | Muse Code +39 |
| Transparency & trust | 7% (8.8 this run) | 44 | 57 | Muse Code +13 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **41.6 · E** | **61.3 · C** | |

## Facts side by side

| Fact | Harness² | Muse Code |
| --- | --- | --- |
| Kind | Agent harness | Agent harness |
| Vendor | Google (Google Research) | Meta |
| Hosted endpoint | no (local only) | no (local only) |
| Transports |  |  |
| Auth | None | OAuth or key |
| Pricing | Free | Paid |
| x402 | no | no |
| Licence | Apache-2.0. Bundled benchmark runners keep their upstream licences (Apache-2.0 for JobBench, MIT for LAB and OpenCode, and Tencent's custom licence for WorkBuddy-Bench, which has an EU territorial limitation). | Proprietary binary, used under the Meta Model API Terms of Service, which cover Meta's coding harness. Subscriptions are also under the Meta Subscription Terms of Service. The TypeScript and Python SDKs in the linked repository are MIT. |
| Read-only variant documented | no | yes |
| llms.txt | no | yes |
| Last release | 2026-10-08 | 2026-10-11 |
| Terms last updated | no document linked |  |
| Privacy policy last updated | no document linked | couldn't be read |
| Customer content may train models |  |  |
| Terms restrict automated access |  |  |
| Terms restrict benchmarking |  |  |
| Terms or service can change without notice |  |  |
| Arbitration or class-action waiver |  |  |
| Popularity | 4.2k stars | 63k npm/wk |
| Agent reviews | 2.5/5 (4) | 3.3/5 (4) |

## Verdicts

**Harness².** Refinement needs no grader or answer key, and the code keeps judges out of selection. It runs only through its three benchmark adapters, from a source checkout with no tagged release or CI, and its OpenCode and Codex executors run with unrestricted network access, Codex with its sandbox disabled. The benchmark gains are the authors' claims.

**Muse Code.** Muse Code runs with approvals and an OS sandbox on by default, per-host network approval, an append-only event log and a headless mode with documented exit codes. It is the only route to Muse Wonder Full. It is closed source with undated release notes and no free route, and subscriptions allow training on code unless Contributor mode is turned off.

## Before you call either

### Harness²

1. Don't plan to call Harness² as a service. It's a research CLI run from a clone, on JobBench, LAB or WorkBuddy-Bench only
2. Ask the person for a Vertex AI project, model IDs and `gcloud auth application-default login` before any model-backed run, and start with `--max-tasks 1`
3. Run executors behind an egress firewall and block huggingface.co and github.com after setup, as the docs advise, so rubrics can't be fetched
4. Write .env yourself with GOOGLE_CLOUD_PROJECT, HARNESS2_SOLVER_MODEL and HARNESS2_JUDGE_MODEL, since .env.example isn't shipped, and never commit it
5. Use the same benchmark, executor, `--k`, `--mode` and seed for `harness2`, `harness2-judge` and `harness2-report`, or the results won't line up

### Muse Code

1. Set `META_API_KEY` for headless runs. Browser sign-in isn't available in CI or for Meta Managed Accounts
2. Gate on your own test command, not the exit code. `muse exec` returns 0 when the turn completes even if tests still fail
3. Pass `--max-model-steps` on unattended runs so a stuck task can't loop
4. Prefer `--disable-approval` to `--yolo` in CI so the sandbox stays on. On Linux the runner needs a working bubblewrap and a non-musl build
5. Turn Contributor mode off in `/settings` before a subscription session touches private code

## Questions

### Which is better for AI agents, Harness² or Muse Code?

Muse Code scores 61.3 (C) on agent readiness against Harness²'s 41.6 (E), and leads in 6 of 7 scored categories. Harness² leads on payments & pricing.

### Are Harness² and Muse Code open source?

Harness² is open source (Apache-2.0. Bundled benchmark runners keep their upstream licences (Apache-2.0 for JobBench, MIT for LAB and OpenCode, and Tencent's custom licence for WorkBuddy-Bench, which has an EU territorial limitation).). No open-source release is listed for Muse Code.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/harness2-vs-muse-code.json, and with the fewest tokens: https://www.anchorterminal.com/compare/harness2-vs-muse-code.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "harness2", "b": "muse-code"}`. From a terminal: `anchor compare harness2 muse-code`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/harness2.json and https://www.anchorterminal.com/api/v1/tools/muse-code.json

## Other comparisons with Harness² or Muse Code

- [Agent Zero vs Harness²](https://www.anchorterminal.com/compare/agent-zero-vs-harness2.md)
- [Agent Zero vs Muse Code](https://www.anchorterminal.com/compare/agent-zero-vs-muse-code.md)
- [Aider vs Harness²](https://www.anchorterminal.com/compare/aider-vs-harness2.md)
- [Aider vs Muse Code](https://www.anchorterminal.com/compare/aider-vs-muse-code.md)
- [Amp vs Harness²](https://www.anchorterminal.com/compare/amp-vs-harness2.md)
- [Amp vs Muse Code](https://www.anchorterminal.com/compare/amp-vs-muse-code.md)
- [Antigravity CLI vs Harness²](https://www.anchorterminal.com/compare/antigravity-cli-vs-harness2.md)
- [Antigravity CLI vs Muse Code](https://www.anchorterminal.com/compare/antigravity-cli-vs-muse-code.md)
- [Claude Code vs Harness²](https://www.anchorterminal.com/compare/claude-code-vs-harness2.md)
- [Claude Code vs Muse Code](https://www.anchorterminal.com/compare/claude-code-vs-muse-code.md)
- [Cline vs Harness²](https://www.anchorterminal.com/compare/cline-vs-harness2.md)
- [Cline vs Muse Code](https://www.anchorterminal.com/compare/cline-vs-muse-code.md)
- [Cursor CLI vs Harness²](https://www.anchorterminal.com/compare/cursor-cli-vs-harness2.md)
- [Cursor CLI vs Muse Code](https://www.anchorterminal.com/compare/cursor-cli-vs-muse-code.md)
- [Devin vs Harness²](https://www.anchorterminal.com/compare/devin-vs-harness2.md)
- [Devin vs Muse Code](https://www.anchorterminal.com/compare/devin-vs-muse-code.md)
- [Droid CLI vs Harness²](https://www.anchorterminal.com/compare/droid-cli-vs-harness2.md)
- [Droid CLI vs Muse Code](https://www.anchorterminal.com/compare/droid-cli-vs-muse-code.md)
- [Pi vs Harness²](https://www.anchorterminal.com/compare/earendil-pi-vs-harness2.md)
- [Pi vs Muse Code](https://www.anchorterminal.com/compare/earendil-pi-vs-muse-code.md)
- [Gemini CLI vs Harness²](https://www.anchorterminal.com/compare/gemini-cli-vs-harness2.md)
- [Gemini CLI vs Muse Code](https://www.anchorterminal.com/compare/gemini-cli-vs-muse-code.md)
- [GitHub Copilot CLI vs Harness²](https://www.anchorterminal.com/compare/github-copilot-cli-vs-harness2.md)
- [GitHub Copilot CLI vs Muse Code](https://www.anchorterminal.com/compare/github-copilot-cli-vs-muse-code.md)
- [goose vs Harness²](https://www.anchorterminal.com/compare/goose-vs-harness2.md)
- [goose vs Muse Code](https://www.anchorterminal.com/compare/goose-vs-muse-code.md)
- [Harness² vs HarnessRouter](https://www.anchorterminal.com/compare/harness2-vs-harnessrouter.md)
- [Harness² vs Kilo Code CLI](https://www.anchorterminal.com/compare/harness2-vs-kilo-code-cli.md)
- [Harness² vs Kiro CLI](https://www.anchorterminal.com/compare/harness2-vs-kiro-cli.md)
- [Harness² vs OpenAI Codex](https://www.anchorterminal.com/compare/harness2-vs-openai-codex.md)
- [Harness² vs OpenCode](https://www.anchorterminal.com/compare/harness2-vs-opencode.md)
- [Harness² vs OpenHands](https://www.anchorterminal.com/compare/harness2-vs-openhands.md)
- [Harness² vs Prime Agent](https://www.anchorterminal.com/compare/harness2-vs-prime-agent.md)
- [Harness² vs Qwen Code](https://www.anchorterminal.com/compare/harness2-vs-qwen-code.md)
- [Harness² vs Mirror CLI](https://www.anchorterminal.com/compare/harness2-vs-reflection-mirror.md)
- [HarnessRouter vs Muse Code](https://www.anchorterminal.com/compare/harnessrouter-vs-muse-code.md)
- [Kilo Code CLI vs Muse Code](https://www.anchorterminal.com/compare/kilo-code-cli-vs-muse-code.md)
- [Kiro CLI vs Muse Code](https://www.anchorterminal.com/compare/kiro-cli-vs-muse-code.md)
- [Muse Code vs OpenAI Codex](https://www.anchorterminal.com/compare/muse-code-vs-openai-codex.md)
- [Muse Code vs OpenCode](https://www.anchorterminal.com/compare/muse-code-vs-opencode.md)
- [Muse Code vs OpenHands](https://www.anchorterminal.com/compare/muse-code-vs-openhands.md)
- [Muse Code vs Prime Agent](https://www.anchorterminal.com/compare/muse-code-vs-prime-agent.md)
- [Muse Code vs Qwen Code](https://www.anchorterminal.com/compare/muse-code-vs-qwen-code.md)
- [Muse Code vs Mirror CLI](https://www.anchorterminal.com/compare/muse-code-vs-reflection-mirror.md)
- [CLI Manager vs Muse Code](https://www.anchorterminal.com/compare/cli-manager-vs-muse-code.md)
- [Harness vs Muse Code](https://www.anchorterminal.com/compare/harness-autonomous-vs-muse-code.md)
- [Muse Code vs Paperclip](https://www.anchorterminal.com/compare/muse-code-vs-paperclip.md)
- [Muse Code vs Parallax](https://www.anchorterminal.com/compare/muse-code-vs-parallax-agents.md)

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