Thread

HarnessTax: How Much Does the Harness Matter for Coding Agents?

233 points · 99 comments · matt_d

lukax · 1789622845 · focus · HN ↗
What matters more is that you use the tools that the target model was fine-tuned on.
E.g. for editing files with Claude models you should use Edit(file_path, old_string, new_string, replace_all) but with GPT models you should use apply_patch_call(patch) (where patch is a custom patch string with custom grammar).
It appears newer models are better at narive harness tool calls and worse at custom tools that look similar to default tools.
<a href="https://lucumr.pocoo.org/2026/7/4/better-models-worse-tools/" rel="nofollow">https://lucumr.pocoo.org/2026/7/4/better-models-worse-tools/
1. nativeit · 1789623558 · focus · HN ↗
  I’m not really a dev, so hefty pinch of salt with this take, but doesn’t this feel like we’re just inventing new “fuzzy” regex with much more required compute?
  1. shepherdjerred · 1789623967 · focus · HN ↗
    comparing LLMs to regex is like the OG dropbox comment (<a href="https://news.ycombinator.com/item?id=9224">https://news.ycombinator.com/item?id=9224).
    I can understand this take 4-5 years ago but I have no idea how that's your position in 2026
  2. raffael_de · 1789631559 · focus · HN ↗
    > inventing new “fuzzy” regex
    not RegEx ... more like a "fuzzy" DSL.

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