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An empirical study of harness design for coding agents

225 points · 59 comments · wek

  1. embedding-shape · · focus · HN ↗
    The conclusions:

    > Planning improves success at additional cost for weaker models but mainly reduces cost, with small decreases in success rate, for stronger models.

    > Predefined tools raise success rates for models with weak bash control, whereas bash-only yields higher success at lower cost for bash-capable models, most clearly on shell-centric task types.

    > context management extends execution trajectories without substantially altering agent behavior and is most beneficial under tight context budgets

    > planning sustains the trajectories of models that abandon tasks too early and trims repeated verification in models that verify too long

    > structured tools support models with limited shell proficiency, while bash-only enables capable models to combine multiple code modifications in a single tool call

    Seems fairly intuitive to me, based on feeling. But also fairly kind of obvious; bash-only tooling has higher success for bash-capable models, compared to using predefined tools for models that aren't good at bash? Yeah... They all seem a bit "duh" to me. The final piece of the conclusion is agreeable regardless of how they arrived at it though:

    > Harness design is thus a conditional systems problem in which each component should be selected for the target model, task type, and resource budget rather than adopted as a default.

    I think lots of people treat the harness/model/prompts combo as interchangeable, but in my experience the quality and efficiently depends heavily on the combo of the harness/model, and using the harness + model made by the same lab, has vastly better experience compared to more "general purpose" (for the lack of a better term) harnesses. Most likely because they use their own traces when training future model iterations.

    1. jimbokun · · focus · HN ↗
      > bash-only tooling has higher success for bash-capable models, compared to using predefined tools for models that aren't good at bash?

      No. The conclusion is that:

      bash-capable models + bash-only tools > bash-capable models + predefined tools

      In other words, MCP was just a bunch of bullshit that maybe helped a little bit until the models got good at bash, and now it's basically useless.

      1. giladkah · · focus · HN ↗

        [dead]

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