A curated, verified, cross-vendor directory of AI agent harnesses — the runtime scaffolding that turns a model into an agent.
◆ 74 harnesses profiled · 9-axis capability schema · last verified 2026-07-08
Formerly OpenDevin, the leading open-source autonomous software-engineering platform: Docker-sandboxed agents that write code, run commands, browse, and open PRs, with a production agent SDK hitting 72% on SWE-bench Verified (Claude Sonnet 4.5) and its own broader OpenHands Index benchmark launched Jan 2026.
VS Code-fork AI IDE whose Agent mode plus in-house Composer models, Background/Cloud Agents (isolated cloud VMs that report back as PRs), hooks, skills, and an agent SDK make it the most fully-built-out commercial agentic IDE; Composer 2 scored 61.7% on Terminal-Bench 2.0 and Composer 2.5 79.8% on SWE-bench Multilingual (SWE-bench Verified not reported).
Copilot's agent mode inside VS Code (extension itself MIT open-sourced; backend service proprietary) iterates on errors, runs tools/terminal, and applies multi-file edits, distinguished by deep GitHub-ecosystem reach: MCP support, SKILL.md Agent Skills (added April 2026), custom .agent.md agents, a multi-vendor model picker with Ollama BYOK, and a cloud 'coding agent' that works issues into PRs on GitHub Actions.