Harnesses Explained: The Inner and Outer Workings of the Coding Agent Harness

chiply•about 11 hours ago

This is a great write up, I specifically love the graph and the distinction between the outer and inner harness.

I often wonder, typically in feverish coding sessions trying to enhance my 'outer harness', how much of this outer harness will eventually be brought into the inner harness? That is, how much of this outer harness engineering will become obsolete very shortly when Claude et al make similar enhancements to the inner harness?

Can you provide any heuristics here? Are there any members of the outer harness that you think are especially worth engineering? Are there others that you think will soon be obviated by upcoming improvements to these agent providers?

Also, I recommend doing a quick proofread of the figure in the article, there are some typos and some bullets seem unfinished. For example "Specificatints" in the outer harness should likely be "Specifications". The bullets under there have a syntactical mistake as well. In the loop part of the image, under "Improve Feedforward" the parenthetical isn't closed and it's an incomplete sentence. There are likely other typos.

paulcaplan•about 9 hours ago

Thank you I greatly appreciate the feedback!!

Wow, yes I should have looked more closely at the image - which was obviously generated by Gemini Nano Banana (it usually does a better job with the text rendering). I checked the article text carefully but not the image...

And that's a great question. I'll answer it in two parts. First, I think the inner and outer are actually quite complimentary. The outer part is largely things that Claude can't provide - such as your own instructions, skills, and ways of validating things specific to your project. I have memory as part of the outer harness but Claude of course does have a memory system and it would not surprise me if they drastically improve it.

The other thing, mentioned in the article, is that harnesses (and specifically Claude) are shrinking: "As I was going through these iteration cycles, we also released Opus 4.6, which provided further motivation to reduce harness complexity. There was good reason to expect 4.6 would need less scaffolding than 4.5 did. ". (from https://www.anthropic.com/engineering/harness-design-long-ru...).

So my* core argument is you still need that "scaffolding", but it belongs in the outer harness.

chiply•about 9 hours ago

Clear, thank you! I didn't know about Nano Banana for this! Would be cool if they let you edit the image text directly, not sure though, I've never used that tool. Impressive that it generated that!

vunderba•about 9 hours ago

NB doesn't support direct editing of an image. But you can open the image in something like Krita or Photoshop, highlight the part you want to change with a red marker, and then ask Nano Banana to modify that highlighted section. It usually does a really good job.

In many cases you can just prompt “change this source text into this target text,” and it works in most cases.

Harnesses Explained: The Inner and Outer Workings of the Coding Agent Harness

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