Getting tons of Error: Failed to decode tool call, did I configure something wrong?

[UrbanFireClash]

Thank you for your great work, I have already get it run! I've managed to get everything running, but during training I keep seeing a lot of:

Error: Failed to decode tool call

Sometimes they appear continuously for quite a while, although the training process itself is still running normally.

I'm not sure if this means I messed up some configuration, or if there's something wrong with the sandbox/tool setup. Is this expected? And if not, how should I fix it?

[YoungZ365]

This is normal and usually does not indicate a configuration problem.

It commonly happens during the early stages of training when the model’s tool-use ability is still relatively weak. At that point, the model frequently generates malformed tool calls or invalid JSON outputs, which then fail during parsing or execution.

These failed tool calls are actually part of the training process. In most cases, they will receive lower rewards, which helps the model gradually learn proper tool formatting and more stable tool usage behavior.

As training progresses and the model becomes better at structured generation and tool interaction, the frequency of these errors will usually decrease significantly.

So if the training loop is still running normally, occasional or even frequent Failed to decode tool call messages early on are generally expected.