SWE-agent jump-started the development of AI agents in 2024. Back then, we placed a lot of emphasis on tools and special interfaces for the agent. However, one year later, as LMs have become more capable, a lot of this is not needed at all to build a useful agent! In fact, the mini agent

• Does not have any tools other than bash — it doesn't even need to use the tool-calling interface of the LMs. This means that you can run it with literally any model. When running in sandboxed environments you also don't need to take care of installing a single package — all it needs is bash.
• Has a completely linear history — every step of the agent just appends to the messages and that's it. So there's no difference between the trajectory and the messages that you pass on to the LM. Great for debugging & fine-tuning.
• Executes actions with subprocess.run — every action is completely independent (as opposed to keeping a stateful shell session running). This makes it trivial to execute the actions in sandboxes (literally just switch out subprocess.run with docker exec) and to scale up effortlessly. Seriously, this is a big deal, trust me.

This makes it perfect as a baseline system and for a system that puts the language model (rather than the agent scaffold) in the middle of our attention. You can see the result on the SWE-bench (bash only) leaderboard, that evaluates the performance of different LMs with mini.

Some agents are overfitted research artifacts. Others are UI-heavy frontend monsters.

The mini agent wants to be a hackable tool, not a black box.

• Simple enough to understand at a glance
• Convenient enough to use in daily workflows
• Flexible to extend

Unlike other agents (including our own swe-agent), it is radically simpler, because it:

• Does not have any tools other than bash — it doesn't even need to use the tool-calling interface of the LMs. Instead of implementing custom tools for every specific thing the agent might want to do, the focus is fully on the LM utilizing the shell to its full potential. Want it to do something specific like opening a PR? Just tell the LM to figure it out rather than spending time to implement it in the agent.
• Executes actions with subprocess.run — every action is completely independent (as opposed to keeping a stateful shell session running). This is a big deal for the stability of the agent, trust me.
• Has a completely linear history — every step of the agent just appends to the messages that are passed to the LM in the next step and that's it. This is great for debugging and understanding what the LM is prompted with.

You should consider mini-swe-agent your default choice. In particular, you should use mini-swe-agent if

• You want a quick command line tool that works locally
• You want an agent with a very simple control flow
• You want even faster, simpler & more stable sandboxing & benchmark evaluations
• You are doing FT or RL and don't want to overfit to a specific agent scaffold

You should use swe-agent if

• You want to experiment with different sets of tools, each with their own interface
• You want to experiment with different history processors

What you get with both

• Excellent performance on SWE-Bench
• A trajectory browser