opencodeCoding Agents

The distinguishing idea is that everything is declared rather than hard-wired: you define named agents in JSON or a markdown file, give each one its own model and its own per-tool permissions — allow, ask or deny for reading, editing and running commands — and switch between them with a keystroke. Two built-in primary agents ship this way, one with full access and one that asks before editing or running anything. It is MIT and provider-agnostic, but it moves fast and it recently changed hands, so old links and pinned versions go stale quickly.

Codex CLICoding Agents

It works the way the other terminal agents do — read the repository, propose changes, run commands — but the boundary it enforces is unusual: on macOS and Linux it uses operating-system sandboxing to restrict which files and commands the agent can reach, so the limit does not depend on the model choosing to respect it. Sign-in runs through a ChatGPT plan or an OpenAI API key, which is the trade: the code is Apache-2.0, the model behind it is not the open part.

PonytailCoding Agents

Ask an agent for a date picker and you can get a dependency, a wrapper component, a stylesheet and a conversation about time zones, when the browser has had `<input type="date">` for years. Ponytail is a single skill aimed at that habit: it pushes the agent towards the smallest thing that works, and towards not writing anything when the platform already provides it. What makes it worth a look rather than a joke is that the maintainers measured it — twelve real tasks on a real repository, with and without the skill — and published the method alongside the numbers, including a note that an earlier, more flattering figure was the per-task ceiling rather than the average.