$ find your agent harness

Anthropic's terminal-native agentic coding tool and the category-defining harness, distinguished by its layered extensibility model (CLAUDE.md memory, Agent Skills, subagents, hooks, plugins, MCP) plus permission modes, checkpoints, and optional sandboxing, available from CLI/IDE/desktop/web with an Agent SDK for building on top.

OpenAI's open-source (Apache-2.0) Rust-rewritten terminal coding agent, distinguished by kernel-level OS sandboxing (Apple Seatbelt on macOS, Landlock/seccomp on Linux), a 272K-1M token context with GPT-5.x Codex models, MCP support, and cloud handoff to Codex web tasks.

The veteran model-agnostic IDE extension (VS Code + JetBrains, strong local-model support) that pivoted to 'Continuous AI' — a cn CLI running markdown-defined async agents as GitHub PR status checks — before being acquired by Cursor in 2026, with the original team shipping a final v2.0.0 (telemetry and auth removed).

Kilo's open-source terminal agent (Kilo CLI 1.0, built on the MIT-licensed OpenCode foundation) distinguished by support for 500+ models with zero-markup BYOK pricing, an MCP marketplace, and cross-surface continuity where a task can move between Slack, VS Code/JetBrains, cloud, and terminal.

The Cline/Roo merger-fork turned all-in-one agentic platform (~26k stars, 3M+ users): IDE extension, CLI, and hosted KiloClaw background agent reachable via Telegram/Discord/Slack, with 500+ models, mid-task model switching, an MCP marketplace, subagents (GA April 2026), and optional Kilo Pass credits from $19/mo.

An early (2023-era) open-source background agent that turned labeled GitHub issues into pull requests by planning, coding and opening a PR asynchronously; the original bot is effectively sunset — the repo README redirects to the company's pivot into a proprietary JetBrains AI plugin (autocomplete + in-IDE agent, $10-60/mo) using Sweep's own LLMs, so the background-agent product itself is legacy.

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.

JetBrains' autonomous coding agent for IntelliJ-family IDEs (plus a Junie CLI that left beta March 2026 with BYOK/OpenRouter routing and CI/CD support), distinguished by leverage of the IDE's code index, a confirmation-gated loop with opt-in 'Brave Mode', Docker/worktree-isolated parallel tasks, remote cloud execution mode, and a companion Claude Agent built on Anthropic's Agent SDK.

OpenAI's delegation-first coding agent whose cloud mode runs each task in an isolated no-internet-by-default sandbox with the repo cloned, opens PRs, does automatic PR code review on GitHub and takes tasks from ChatGPT/Slack, bundled into ChatGPT Plus/Pro/Business with rolling credit-based billing since April 2026 (the CLI companion is open source, the cloud service is not).

YC-backed autonomous software engineer that picks up tickets from GitHub/Jira/Linear and opens tested PRs end-to-end across CLI, desktop, VS Code and cloud, distinguished by its own in-house Lumen model family (including on-device Scout and air-gapped sovereign variants for regulated industries like HSBC/NatWest/BAE) and the April 2026 'Swarm' feature for parallel long-horizon agents; credit-based seats at $20 (Hobby) and $200 (Professional).