AI Harness Leaderboard

What runs the loop. The programs that hold a model, its tools and its permissions together for long enough to finish a job. There is no composite score here: harness quality depends on the job, so this board compares what each tool is, how it isolates work and who it is for. Tap any column to re-sort.

⚙ How to read this board

Not a score. Judgement calls on what each harness is for, checked against vendor docs.

Order is editorial. Open any row for its full spec sheet.

#	Harness	Interface	License	Isolation	Best for
1	Claude Codecoding AnthropicTerminal, desktop, web and IDE. The reference implementation of a coding agent with real permissions.	Terminal, desktop, web, IDE	Proprietary (Anthropic)	Permissioned tools, opt-in sandbox	A coding agent with real permissions
2	Claude Agent SDKlibrary AnthropicClaude Code's loop, tools and context management as a library. Python and TypeScript only — other languages drive the CLI as a subprocess.	Imported library	Proprietary (Anthropic)	Inherits the host process	Building custom agents on Claude Code's loop
3	Managed Agentshosted AnthropicHosted REST API for long-running agents. Anthropic runs the agent and the sandbox, so you don't operate session infrastructure.	REST API	Proprietary, hosted	Anthropic-run sandbox	Long-running agents without running infra
4	Codex CLIcoding OpenAISandboxed by default and open source. The usual pick when those two are hard requirements.	Terminal	Open source	Sandboxed by default	Open-source + sandbox as hard requirements
5	Gemini CLIcoding GoogleApache-2.0, strong on whole-repository context. The free tier ended 18 Jun 2026, so it's now a budgeted decision.	Terminal	Apache-2.0	Configurable	Whole-repository context (now paid)
6	Editor agentsin-editor Cursor, Zed, Copilot, othersAgent loops living inside the editor. Tighter feedback, narrower blast radius.	IDE integration	Mixed / proprietary	Editor workspace	Tight feedback with a narrow blast radius
7	Hermes Agentagent open source · self-hostedAn always-on agent for small businesses: it watches a mailbox, form or queue and acts on what lands. Covered in our setup and small-business guides.	Self-hosted service	Open source	Your own host	Always-on mailbox / queue automation
8	OpenClawcoding open sourceOpen-source, model-agnostic terminal coding agent — Claude Code's ergonomics without the lock-in, MIT-licensed.	Terminal	MIT	Permissioned tools	Claude Code ergonomics without lock-in
9	Ampcoding SourcegraphAgentic coding built for big codebases, with deep repository search sitting behind the loop.	CLI + editor	Proprietary (Sourcegraph)	Workspace	Large codebases with deep search
10	OpenCodecoding open sourceProvider-agnostic terminal agent: bring any model, keep the same loop and permissions.	Terminal	Open source	Permissioned tools	One loop across any model
11	Prime Agentcoding Prime IntellectSelf-improving harness: one persistent Python kernel as the only tool	Terminal + ACP	MIT	Background subagent sessions	Long-horizon self-improving work
12	DeepSeek Harnesscoding DeepSeekEverything is a plugin — including the agent loop	Terminal	MIT	OS-level sandbox + session log	Assembling a harness from parts
13	OpenHandscoding All-Hands AIFormerly OpenDevin: self-hosted, sandboxed, model-agnostic	Terminal + web	MIT	Optional Docker sandbox	Self-hosted automation you can audit
14	Gooseagent Agentic AI FoundationBlock's agent, now under Linux Foundation governance	Desktop + CLI + API	Apache-2.0	Local runtime, MCP extensions	Provider-agnostic work on your machine
15	Qwen Codecoding QwenLM (Alibaba)Gemini CLI lineage, tuned for Qwen models	Terminal	Apache-2.0	Configurable	Running Qwen models in a strong loop
16	Aidercoding Aider-AIGit-native pair programmer: one commit per edit	Terminal	Apache-2.0	Git-tracked edits	Short supervised runs with clean history
17	Picoding earendil-worksMinimal harness: a system prompt under a thousand tokens	Terminal	Open source	Permissioned tools	A minimal harness over a strong model
18	Grok Buildcoding xAIxAI's harness: memory that survives between sessions	Terminal + web + mobile	Harness open-sourced	Hosted service + CLI	High-volume coding on a subscription
19	GitHub Copilot CLIcoding GitHubGitHub-native terminal agent with auto model routing	Terminal	Proprietary	Permissioned tools + GitHub context	Teams living in GitHub and Copilot seats

Showing 19 of 19 harnesses

19 spec sheets · click a name to open one

Editorial index · hand-maintained, not a feed

Hand-maintained, not a feed. Checked 26 Sep 2026 against Anthropic's model docs, OpenAI's model list and Google's Gemini docs. Vendor facts come from those pages; the read on each harness is judgement, not vendor copy.