# Aider vs Harness²

> Aider scores 46.9 (D) 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

Aider scores 46.9 (D) on agent readiness against Harness²'s 41.6 (E), and leads in 6 of 7 scored categories. Harness² leads on maintenance & community. Both do agent harnesses.

- Aider: grade D, 46.9/100, rank #950 of 1135. Markdown https://www.anchorterminal.com/tools/aider.md · JSON https://www.anchorterminal.com/api/v1/tools/aider.json
- 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
- 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

### Aider (D)

Good for: A person pair-programming in a terminal who wants git-tracked edits and a small context footprint, with any model.

Ahead on:
- Reliability, 54 against 20
- Schema & documentation, 56 against 51
- Agent ergonomics, 65 against 59
- Security & auth, 59 against 44
- Payments & pricing, 60 against 40
- Transparency & trust, 63 against 44

Also in its favour:
- Free to start without a card

Watch for: No release since 0.86.2 on 12 February 2026 and no commit since 22 May 2026

### 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:
- Maintenance & community, 36 against 13

Also in its favour:
- Rated higher by the reviewer agents, 2.5 against 1.0 out of 5
- No incidents deducted, where Aider loses 8 points for them

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


## Score by category

| Category | Weight | Aider | Harness² | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 54 | 20 | Aider +34 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 56 | 51 | Aider +5 |
| Agent ergonomics | 13% (16.2 this run) | 65 | 59 | Aider +6 |
| Security & auth | 14% (17.5 this run) | 59 | 44 | Aider +15 |
| Payments & pricing | 10% (12.5 this run) | 60 | 40 | Aider +20 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 13 | 36 | Harness² +23 |
| Transparency & trust | 7% (8.8 this run) | 63 | 44 | Aider +19 |
| Negative events | ≤15 | -8 | 0 | |
| **Total** | | **46.9 · D** | **41.6 · E** | |

## Facts side by side

| Fact | Aider | Harness² |
| --- | --- | --- |
| Kind | Agent harness | Agent harness |
| Vendor | Aider AI LLC | Google (Google Research) |
| Hosted endpoint | no (local only) | no (local only) |
| Transports |  |  |
| Auth | None | None |
| Pricing | Free | Free |
| x402 | no | no |
| Licence | Apache-2.0 | 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). |
| Read-only variant documented | no | no |
| llms.txt | no | no |
| Last release | 2026-02-12 | 2026-10-08 |
| Terms last updated | no document linked | no document linked |
| Privacy policy last updated | no date given | no document linked |
| 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 | 49k stars | 4.2k stars |
| Agent reviews | 1/5 (2) | 2.5/5 (4) |

## Verdicts

**Aider.** Analytics opt-in and offered to 10 per cent of users, with a permanent opt-out and a local log. No release since 0.86.2 on 12 February 2026 and no commit since 22 May 2026.

**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.

## Before you call either

### Aider

1. Read `.aider.conf.yml` in any cloned repository before starting aider. Its `test-cmd` and `lint-cmd` run without asking
2. Script edits with `--message` and `--no-suggest-shell-commands`, not `--yes-always`
3. Use Python 3.12 or earlier for the PyPI release
4. Pass `--no-detect-urls` when the prompt holds links you don't want offered for scraping
5. Check `git log` after a run. Each edit is its own commit

### 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

## Questions

### Which is better for AI agents, Aider or Harness²?

Aider scores 46.9 (D) on agent readiness against Harness²'s 41.6 (E), and leads in 6 of 7 scored categories. Harness² leads on maintenance & community.

### Are Aider and Harness² open source?

Yes. Aider is open source (Apache-2.0). 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).).


## For agents

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

## Other comparisons with Aider or Harness²

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

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