Repository: explodinggradients/ragas
Issue: Explicit the "Failed to parse output. Returning None." of RagasoutputParser or add a way to catch it. 
Root cause: Documentation Deficiency

**Describe the Feature**
Hi @shahules786 @jjmachan, I'm back in Ragas business ^^

I've recently stumble upon a `Failed to parse output. Returning None.` while trying to evaluate the faithfulness of answers generated from a model based on a generated dataset.

As explained in the warning, it seems to come from a ill structured output. After looking in your repository, I've noticed many issues related to this warning and its consequences.

Some users have found different solutions as changing the evaluation prompt (#1150) or the context/output max token (#1120) but for me it was thanks to @jjmachan [answer](https://github.com/explodinggradients/ragas/issues/1120#issuecomment-2257624354) that I've managed to correctly evaluate my rag by changing the llm metric from `llama3.1:8b` to `llama3.2:3b` (I use LangChain wrapper to wrap a model provided by Ollama with ChatOllama).

However, there still are many opened issues concerning this same warning (#1630, #1545, #1358, #1274, #1228, #1206, #1186, #1150, #1120, #966, #957, #955, #859)

That's why I was wondering if you could explicit a bit more this warning to guide users along some way to improve their evaluation method or change the warning into an exception so we can raise it if needed and explicit the issue ourselves.

**Why is the feature important for you?**
So others won't spend so much time to debug their evaluation step and avoid adding useless issues to your repository ^^


In any case, thanks again for your amazing work, keep it up as long as possible ! Have a nice day :)

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> **Describe the Feature** Hi @shahules786 @jjmachan, I'm back in Ragas business ^^
> 
> I've recently stumble upon a `Failed to parse output. Returning None.` while trying to evaluate the faithfulness of answers generated from a model based on a generated dataset.
> 
> As explained in the warning, it seems to come from a ill structured output. After looking in your repository, I've noticed many issues related to this warning and its consequences.
> 
> Some users have found different solutions as changing the evaluation prompt (#1150) or the context/output max token (#1120) but for me it was thanks to @jjmachan [answer](https://github.com/explodinggradients/ragas/issues/1120#issuecomment-2257624354) that I've managed to correctly evaluate my rag by changing the llm metric from `llama3.1:8b` to `llama3.2:3b` (I use LangChain wrapper to wrap a model provided by Ollama with ChatOllama).
> 
> However, there still are many opened issues concerning this same warning (#1630, #1545, #1358, #1274, #1228, #1206, #1186, #1150, #1120, #966, #957, #955, #859)
> 
> That's why I was wondering if you could explicit a bit more this warning to guide users along some way to improve their evaluation method or change the warning into an exception so we can raise it if needed and explicit the issue ourselves.
> 
> **Why is the feature important for you?** So others won't spend so much time to debug their evaluation step and avoid adding useless issues to your repository ^^
> 
> In any case, thanks again for your amazing work, keep it up as long as possible ! Have a nice day :)

i still have this issue. also the thing is that I already have the embeddings and textual data. so I created the subclass to bypass the API error call. but still I see the message. I think the reason that cause fail to parse the output is that we use the "prompt value"
in the subclass and while we feed our own textual data it can not match and we see the message.

> **Describe the Feature** Hi @shahules786 @jjmachan, I'm back in Ragas business ^^
> 
> I've recently stumble upon a `Failed to parse output. Returning None.` while trying to evaluate the faithfulness of answers generated from a model based on a generated dataset.
> 
> As explained in the warning, it seems to come from a ill structured output. After looking in your repository, I've noticed many issues related to this warning and its consequences.
> 
> Some users have found different solutions as changing the evaluation prompt (#1150) or the context/output max token (#1120) but for me it was thanks to @jjmachan [answer](https://github.com/explodinggradients/ragas/issues/1120#issuecomment-2257624354) that I've managed to correctly evaluate my rag by changing the llm metric from `llama3.1:8b` to `llama3.2:3b` (I use LangChain wrapper to wrap a model provided by Ollama with ChatOllama).
> 
> However, there still are many opened issues concerning this same warning (#1630, #1545, #1358, #1274, #1228, #1206, #1186, #1150, #1120, #966, #957, #955, #859)
> 
> That's why I was wondering if you could explicit a bit more this warning to guide users along some way to improve their evaluation method or change the warning into an exception so we can raise it if needed and explicit the issue ourselves.
> 
> **Why is the feature important for you?** So others won't spend so much time to debug their evaluation step and avoid adding useless issues to your repository ^^
> 
> In any case, thanks again for your amazing work, keep it up as long as possible ! Have a nice day :)

when I use old module——from langchain_community.llms import Ollama，it did 'Failed to parse output. Returning None.', and use 'from langchain_ollama import ChatOllama'，it's not occurs , but "unable to apply transformation: AsyncClient.chat() got an unexpected keyword argument 'temperature'"

> > **Describe the Feature** Hi [@shahules786](https://github.com/shahules786) [@jjmachan](https://github.com/jjmachan), I'm back in Ragas business ^^
> > I've recently stumble upon a `Failed to parse output. Returning None.` while trying to evaluate the faithfulness of answers generated from a model based on a generated dataset.
> > As explained in the warning, it seems to come from a ill structured output. After looking in your repository, I've noticed many issues related to this warning and its consequences.
> > Some users have found different solutions as changing the evaluation prompt ([#1150](https://github.com/explodinggradients/ragas/issues/1150)) or the context/output max token ([#1120](https://github.com/explodinggradients/ragas/issues/1120)) but for me it was thanks to [@jjmachan](https://github.com/jjmachan) [answer](https://github.com/explodinggradients/ragas/issues/1120#issuecomment-2257624354) that I've managed to correctly evaluate my rag by changing the llm metric from `llama3.1:8b` to `llama3.2:3b` (I use LangChain wrapper to wrap a model provided by Ollama with ChatOllama).
> > However, there still are many opened issues concerning this same warning ([#1630](https://github.com/explodinggradients/ragas/issues/1630), [#1545](https://github.com/explodinggradients/ragas/issues/1545), [#1358](https://github.com/explodinggradients/ragas/issues/1358), [#1274](https://github.com/explodinggradients/ragas/issues/1274), [#1228](https://github.com/explodinggradients/ragas/issues/1228), [#1206](https://github.com/explodinggradients/ragas/issues/1206), [#1186](https://github.com/explodinggradients/ragas/issues/1186), [#1150](https://github.com/explodinggradients/ragas/issues/1150), [#1120](https://github.com/explodinggradients/ragas/issues/1120), [#966](https://github.com/explodinggradients/ragas/issues/966), [#957](https://github.com/explodinggradients/ragas/issues/957), [#955](https://github.com/explodinggradients/ragas/issues/955), [#859](https://github.com/explodinggradients/ragas/issues/859))
> > That's why I was wondering if you could explicit a bit more this warning to guide users along some way to improve their evaluation method or change the warning into an exception so we can raise it if needed and explicit the issue ourselves.
> > **Why is the feature important for you?** So others won't spend so much time to debug their evaluation step and avoid adding useless issues to your repository ^^
> > In any case, thanks again for your amazing work, keep it up as long as possible ! Have a nice day :)
> 
> when I use old module——from langchain_community.llms import Ollama，it did 'Failed to parse output. Returning None.', and use 'from langchain_ollama import ChatOllama'，it's not occurs , but "unable to apply transformation: AsyncClient.chat() got an unexpected keyword argument 'temperature'"

I have the exact same problem (TypeError: AsyncClient.chat() got an unexpected keyword argument 'temperature'). Is there a solution for this? Where should I pass the temperature parameter?

I am having similar issues
 ("OutputParserException(Failed to parse StringIO from completion" and also "OutputParserException(Invalid json output:"),

 but less frequently now.

I'm using RAGAS 0.3.5 and my evaluator models were llama3.1-8B-instruct and qwen2.5-14B-Instruct. I find that instruct models are less likely to give this related errors. Also, my evaluations got better results with the qwen model (probably because of the complexity of the model, but I guess there is a case of study in RAGAS which is the use of local models, specially Small Language Models and it's limitations of acting as judges

I also improved the max_model_len to 16/32k tokens and increased max_tokens on the LLM wrapper.

But RAGAS is really giving me the chills, specially because my evaluations are not being that great when they should :/