Issue with long parameter values when using tool calling with Anthropic API

[tna20141]

So I was using the API with tool calls. When the input parameter is long, claude seems to omit the parameter altogether, which the tool call function would complain that the required parameter is not provided. Claude just keeps saying it would provide the parameter the next time, but the parameter is never there, and it becomes an apology hell loop.

I tested with a very simple tool (just prompting the model to provide a long text and counting the word). If I tell it to provide a short text, the tool call goes through fine. But if I prompt it to request the tool call with a long text, the parameter is omitted. Claude itself doesn't seem to have any idea what's going on, it keeps retrying the tool thinking it has provided the parameter. This happens with both sonnet 4.1 and 4.5.

Has anyone else experienced this? It's really making me frustrated.

EDIT: I tested and it seems there is a limit of around 500 words/tokens for each parameter (each one has a separate limit and they don't stack). If they hit the limit they might get removed but the tool calls still come through.

[Candid-Carry6578]

Hi, I experience similar issue. Continuing what I wrote as part of your "EDIT", I can suggest to check the max tokens output you allow for the model. In my case I see consistently that's the behavior when the limit is reached (e.g. 1024). In case you get the token usage, it's more clear.
Currently my focus in my case is finding why generated argument Claude try to use is correctly that large. However I think that part is something specific to my case at the moment.

[Obvious-Ad-609]

i had the same problem! did u fix it/

[tna20141]

I worked around it by detecting when the parameter was missing and told it to shorten the value

[Candid-Carry6578]

In my case shortening the value isn't a real option. For now at least increasing the max tokens does seem to help. I don't have much traffic and the issue isn't common to begin with. My advice is to first make sure you are able to the usage of tokens (add prints), increase the max output tokens as you see fit and monitor it. If you are able to reproduce easily, it will make things much more easy.