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Optimizing Tool Selection for LLM Workflows with Differentiable Programming

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Re: Optimizing Tool Selection for LLM Workflows with Differentiable Programming

#11
post #2

I was experimenting with how local, learnable routers can reduce token overhead, and lower costs, and decided to publish a post about it. The main goal is to delegate tool calls via a PyTorch based learner and examples of how to integrate this into a DSPy pipeline. Feedback welcome!

Creative. You’ve given me some ideas. Thanks!

Re: Optimizing Tool Selection for LLM Workflows with Differentiable Programming

#12
I don’t think the problem is “how to optimise tool selection for the LLM”. I think the real problem is using an LLM to do tool selection at all. This is control flow and I believe should be handled with hardcoded rules and/separation of concerns.

If LLMs could handle determinism better, I’d say having a single chat-based entrypoint into a plethora of services makes sense. But as they stand, it doesn’t make sense. Simpler control flow and constraining the number and type of downstream services that sit behind a single interface I think is the way to go.

That said, I agree we should keep the ambition to move to the one size fits all approach.

Re: Optimizing Tool Selection for LLM Workflows with Differentiable Programming

#13
post #2

I was experimenting with how local, learnable routers can reduce token overhead, and lower costs, and decided to publish a post about it. The main goal is to delegate tool calls via a PyTorch based learner and examples of how to integrate this into a DSPy pipeline. Feedback welcome!

Thanks for the informative and inspiring post! This is definitely cool, and I can imagine very useful.

However I do want to mention that the “recommended” flow these days isn’t to separate out a tool request in the way you have. Eg instead of asking an LLM to route a tool, extracting that, running the tool, passing output back to the LLM, etc. - you simply pass the tool definitions, prompt, structural output expectations, and let the LLM (and your caller library) manage the tool use loop.

That’s how these modern LLMs are trained in post-training, and so I suspect it’s likely you’ll get different (and potentially worse?) results in trying to subvert this with a small, local model.

It comes with all the downsides you mentioned to let the LLM do this, but is also more likely to be in-distribution, and it’s easier to compose multiple tool calls.

Anyway, thanks for sharing! I’d love to see evals on a task where it compares the result when an LLM is involved in tool selection versus when it is handed tool output only - if I’m wrong about quality degradation then there’s a lot to like about your local tool routing.

Re: Optimizing Tool Selection for LLM Workflows with Differentiable Programming

#14
I have been thinking a lot about tool selection lately, and something that I keep repeating to myself is: "the LLM has intuition, but I have data".

I guess that applies when you're not able to fine-tune the LLM you're using. Presumably Anthropic has a lot of data too.

Re: Optimizing Tool Selection for LLM Workflows with Differentiable Programming

#16
post #5

Is selection really the issue? You'd still need to figure out what payload to give to the tool based on your context. But I guess depending on your business case it might be worth it. It's not something I'd do from the beginning, though.

This is a bigger problem than it looks like at first glance. For isecases where llm + tool calls make more sense compared to say llm assisted codegen, figuring out the tool arguments is nontrivial. Where it is relatively easy I think codegen is a better option wrt amortised running costs

Re: Optimizing Tool Selection for LLM Workflows with Differentiable Programming

#17
post #2

I was experimenting with how local, learnable routers can reduce token overhead, and lower costs, and decided to publish a post about it. The main goal is to delegate tool calls via a PyTorch based learner and examples of how to integrate this into a DSPy pipeline. Feedback welcome!

Thanks for the informative and inspiring post! This is definitely cool, and I can imagine very useful. However I do want to mention that the “recommended” flow these days isn’t to separate out a tool request in the way you have. Eg instead of asking an LLM to route a tool, extracting that, running the tool, passing output back to the LLM, etc. - you simply pass the tool definitions, prompt, structural output expectat…

great point, appreciate the comment. totally agree with your framing, though i think there’s still a gap in how tool use is handled today.

quick note: it doesn’t have to be an rnn. i’ve got a follow-up example coming that uses a transformer-style ToolController with self attention, more expressive routing, etc.

but here’s the thing — when you rely on few-shot bootstrapping the LLM, you never end up updating the model's priors. even after 100k tool calls, you’re still stuck in the same polluted context window and its all stateless.

this gets worse fast with more than 3–4 tool calls, especially when there’s branching logic (e.g., if api1 > 5, go left, else right).

what this approach offers is: backprop through tool calls. you can tune prompts and update priors across the full workflow, end to end. trying to develop this intuition a bit more, and would love feedback.

thanks for the suggestion on the eval — will post that comparison soon.

Re: Optimizing Tool Selection for LLM Workflows with Differentiable Programming

#18
post #3
post #2

I was experimenting with how local, learnable routers can reduce token overhead, and lower costs, and decided to publish a post about it. The main goal is to delegate tool calls via a PyTorch based learner and examples of how to integrate this into a DSPy pipeline. Feedback welcome!

I think this is a creative approach. I wonder how the success rates for that little RNN compare to the success rates of the primary LLM, especially for complex queries or complex tool calls. At some point you have to scale that network up large enough to get better results. Eventually you've come back around and you might as well use an LLM. I think a similar approach with potentially better results (depends on the a…

thank you, appreciate the comment! thats a great point -- as I'm developing this intuition, I'm designing an eval which does a comparison of the openAI example there + tool call using a simple RNN + one that uses an encoder model. would love more feedback (on blog / X etc) when I post.

Re: Optimizing Tool Selection for LLM Workflows with Differentiable Programming

#19
post #2

I was experimenting with how local, learnable routers can reduce token overhead, and lower costs, and decided to publish a post about it. The main goal is to delegate tool calls via a PyTorch based learner and examples of how to integrate this into a DSPy pipeline. Feedback welcome!

Can you put all of the code into a gist or something?

yes apologies, the code rendering in substack wasn't great, but I'll put this in a gist!

Re: Optimizing Tool Selection for LLM Workflows with Differentiable Programming

#20
post #7
post #2

I was experimenting with how local, learnable routers can reduce token overhead, and lower costs, and decided to publish a post about it. The main goal is to delegate tool calls via a PyTorch based learner and examples of how to integrate this into a DSPy pipeline. Feedback welcome!

Nit - code screenshots are a PITA to read on mobile!

ty for the feedback, yes, balancing bad code blocks on substack vs making it look pretty lol. I'll post code next time.
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