gemini doesn't handle edit tool very well

[adamdotdevin]

it fails a lot with "oldString not found in file. Make sure it matches exactly, including whitespace and line breaks". could be something we could fix with whitespace normalization?

[monotykamary]

It also happened quite frequently in the old, we don't talk about anymore, opencode. It worked slightly better with patch, but at around 70k+ token context, it fails quite persistently on it and edit.

We actually have quite a few options: Aider has diff-fenced, avante.nvim has a poor man's cursor apply, and one guy made CEDARScript for Gemini back before it was cool. I think the core elements in CEDARScript could be something we can adapt for our case; like offloading precise line numbers, indentation counts, add whitespace to that, and syntax consistency to a runtime.

To add on, Gemini 2.5 Pro/Flash also worked with a lot less errors on Cline's XML tool calling, not sure whether we should consider that in the near future.

[GitMurf]

it fails a lot with "oldString not found in file. Make sure it matches exactly, including whitespace and line breaks". could be something we could fix with whitespace normalization?

I experimented a while back with fixing this issue with Claude code by creating my own mcp server edit tool. It was quite hacky but ultimately the two conclusions I came to:

1. As you alluded to @adamdotdevin the most success I found was with simply scrubbing the indentations (both in kind like tabs vs spaces, and in size like 2 vs 4 spaces). I used the "trimming" as a way to match / find the old content but then would still replace correctly with the real new content with actual indents provided by LLM.

2. I am not sure if you use line numbers at all with the opencode edit tool but if you do, LLMs are horrid at line numbers. They often skip over empty lines so the line numbers they consider are off kilter. If you use line numbers at all, I suggest just using it as a safety net in case there are multiple matches in the same file of the old content string, but if only one is found anyways, the line numbers don't matter so just replace it. Or maybe you don't use line numbers and this doesn't matter.

Hope this helps!

[thdxr]

@GitMurf so i'm going to implement an alternate edit tool for gemini - we have the ability to swap tools out automatically per provider

can you explain more what you mean by scrubbing the indentations? like you'd trim every line in the file, old string, new string and do the replace?

[GitMurf]

can you explain more what you mean by scrubbing the indentations? like you'd trim every line in the file, old string, new string and do the replace?

Great question! Sorry I wasn't very clear. If LLM passes back an "old string" to match on to replace of the following:

    const foo = "bar";
    const bar = "baz";

Then instead of looking for that string with the indentation, I would look for the following:

const foo = "bar";
const bar = "baz";

Now as you alluded to, you'd essentially have to trim the entire file indents too if you wanted to try and do a full string match on this successfully. But I thought that was excessive. So the way I did it is I start by iterating through the lines of the real file, trimming each line as I check it and look for a match to the first line provided by the LLM (const foo = "bar";) ... if I find a match at line 27 then I try matching lines 2...n (in my example above it would just be matching the next trimmed line of const bar = "baz";).

If there happened to be two of the same old strings in the file, this also by default would replace the first found occurrence so that you can instruct the user this is the expectation in the rare case they have the same content multiple times in the file.

TLDR:

1. Split the old string match coming from LLM into array of lines.
2. Trim the indentations from incoming LLM old string lines.
3. Loop through real file lines looking for a match to the first line coming from LLM (trimming to match).
4. When first line is found, then loop through the other lines provided to see if they also match trimmed.

The other thing to note is I actually instructed the LLM to provide its old content and new content info each as an array of lines to avoid needing to split the content string by line break.

Also I first actually checked for exact match and edited the file with exact match if found. I only did the trimming logic as a fallback if a match wasn't found.

Does this make sense? Let me know if you have any questions and also would be happy to review any code you put together.

[GitMurf]

Also @thdxr fyi it may be useful to allow the user to choose the tool to use as for me, gpt-4.1 also has been having some issues with the old string matching with edit tool so I could see other non Gemini models also want to still try this other implementation of edit tool.

[moda20]

hey, i am having the same old string issue consistently when using ollama/qwen3. so it(s not just a gemeni thing

[BigMitchGit]

perhaps it'd be good to implement a separate edit model that the user can choose. One model for the reasoning and coming up with changes, and another model for the sole purpose of applying the edit.

Then let the user choose what model to use there (i.e. self-hosted fastapply, morph fast apply, relace instant apply, llama3.3-70b, or any other model) and make it do whole or diff edits similar to what aider does?

[JamesMowery]

I can also confirm that while using both ollama and llama.cpp with qwen2.5-coder and qwen3 that I'm also constantly getting this "Error: oldString not found in content or was found multiple times" (or errors extremely similar to this; I've seen the one posted by OP as well).

[codemonkey76]

I'm using Claude Sonnet 4, and getting this regularly:
Error: oldString and newString must be different

[moda20]

@codemonkey76 this also happens with local, and gemeni, models too

[moshemarciano]

got this error today with grok/kimi-k2
it actually went into an infinite loop sending the same payload to the llm again and again, I stopped it after 20 times

same tool call and string:

Error: oldString and newString must be different

[esafak]

I can reliably trigger this error with a variety of models; I don't think it's provider specific.

[benmerckx]

This seems to be all I'm getting on macos. Model tries to edit, this errors pops up, makes the same text insertion and starts all over.
Edit: with chatgpt o4-mini