[BUG] Error message for apply_diff tool use lacks clarity and example #9113
Description
Problem (one or two sentences)
When attempting to use Roo Code with MoonshotAI/kimi-k2-instruct-0905, the platform shows an error for the apply_diff tool regarding missing arguments (file element), but the error message does not clearly indicate what part of the XML structure is incorrect or provide an example of correct usage. The message only states: "Missing value for required parameter 'args (must contain at least one valid file element). Please retry with complete response." This makes it difficult to resolve the issue or guide the model to fix its output
Context (who is affected and when)
Anyone using Roo Code with capable language models (like MoonshotAI/kimi-k2-instruct-0905) for coding or file-editing tasks may encounter tool execution failures (particularly for apply_diff) when the model’s response does not match expected XML format. The error response from Roo Code does not help the model (or even the user) understand what needs to be changed, slowing down troubleshooting and productivity.
Reproduction steps
- Set up Roo Code with MoonshotAI/kimi-k2-instruct-0905 as the model provider.
- Request the model to edit an existing file using the apply_diff tool.
- Observe Roo Code’s error response regarding missing value for required parameter 'args'.
- Inspect the error output - note that there is no clear indication or example of the correct XML structure required for successful tool invocation.
Expected result
If the model tried using apply_diff and failed in using it correctly, then roo code should give example to the model on how to use apply_diff correctly and also it should tell what was the specific error in detail.
Actual result
If the model tried using apply_diff and failed in using it correctly, the roo code is just sending a brief unclear error to the model and is just giving example of how to use attempt_completion tool which is irrelevant here because the model had tried using apply_diff. This current behaviour is just leading to retries with no improvement and in the end I get this message:
This may indicate a failure in the model's thought process or inability to use a tool properly, which can be mitigated with some user guidance (e.g. "Try breaking down the task into smaller steps").
This is not model's limitation, this is roo code's limitation. The model is capable enough, only roo code is not being able to provide the context to the model in a better way. Read: Why Do Agents Fail?
Variations tried (optional)
No response
App Version
3.30.3
API Provider (optional)
None
Model Used (optional)
MoonshotAI/kimi-k2-instruct-0905
Roo Code Task Links (optional)
No response
Relevant logs or errors (optional)
**User:**
[attempt_completion] Result:
The user has provided feedback on the results. Consider their input to continue the task, and then attempt completion again.
<feedback>
you used "@wrapModelCall" in the md file. check the docs of langchain ts again, there is no such thing as "@"
</feedback>
<environment_details>
# VSCode Visible Files
# VSCode Open Tabs
# Current Time
Current time in ISO 8601 UTC format: 2025-11-08T05:58:53.801Z
User time zone: Asia/Calcutta, UTC+5:30
# Current Cost
$0.00
# Current Mode
<slug>code</slug>
<name>💻 Code</name>
<model>moonshotai/kimi-k2-instruct-0905</model>
You have not created a todo list yet. Create one with `update_todo_list` if your task is complicated or involves multiple steps.
</environment_details>
---
**Assistant:**
You're absolutely right! I need to fix the decorator syntax in the markdown file. Let me correct that and update the documentation with the proper TypeScript syntax.
<apply_diff>
<args>
<file>
<path>langchain-middleware-examples.md</path>
</file>
<diff>
<content>
<<<<<<< SEARCH
### Decorator-based Middleware (Simple Hooks)
import { createAgent, beforeModel, afterModel, wrapModelCall } from "langchain";
// Node-style: logging before model calls
@beforeModel
const logBeforeModel = (state, runtime) => {
console.log(`About to call model with ${state.messages.length} messages`);
return null; // Return null to continue normally
};
// Node-style: validation after model calls
@afterModel
const validateOutput = (state, runtime) => {
const lastMessage = state.messages[state.messages.length - 1];
if (typeof lastMessage.content === 'string' && lastMessage.content.includes("BLOCKED")) {
return {
messages: [...state.messages, { role: "assistant", content: "I cannot respond to that request." }]
};
}
return null; // Return null to continue normally
};
// Wrap-style: retry logic
@wrapModelCall
const retryModel = (request, handler) => {
for (let attempt = 0; attempt < 3; attempt++) {
try {
return handler(request);
} catch (e) {
if (attempt === 2) throw e;
console.log(`Retry ${attempt + 1}/3 after error: ${e}`);
}
}
};
const agent = createAgent({
model: "gpt-4o",
tools: [webSearch, calculator],
middleware: [logBeforeModel, validateOutput, retryModel],
});
=======
### Simple Function-based Middleware
import { createAgent, beforeModel, afterModel, wrapModelCall } from "langchain";
// Node-style: logging before model calls
const logBeforeModel = beforeModel((state, runtime) => {
console.log(`About to call model with ${state.messages.length} messages`);
return null; // Return null to continue normally
});
// Node-style: validation after model calls
const validateOutput = afterModel((state, runtime) => {
const lastMessage = state.messages[state.messages.length - 1];
if (typeof lastMessage.content === 'string' && lastMessage.content.includes("BLOCKED")) {
return {
messages: [...state.messages, { role: "assistant", content: "I cannot respond to that request." }]
};
}
return null; // Return null to continue normally
});
// Wrap-style: retry logic
const retryModel = wrapModelCall((request, handler) => {
for (let attempt = 0; attempt < 3; attempt++) {
try {
return handler(request);
} catch (e) {
if (attempt === 2) throw e;
console.log(`Retry ${attempt + 1}/3 after error: ${e}`);
}
}
});
const agent = createAgent({
model: "gpt-4o",
tools: [webSearch, calculator],
middleware: [logBeforeModel, validateOutput, retryModel],
});
>>>>>>> REPLACE
</content>
</diff>
</apply_diff>
---
**User:**
[apply_diff for 'langchain-middleware-examples.md'] Result:
The tool execution failed with the following error:
<error>
Missing value for required parameter 'args (must contain at least one valid file element)'. Please retry with complete response.
# Reminder: Instructions for Tool Use
Tool uses are formatted using XML-style tags. The tool name itself becomes the XML tag name. Each parameter is enclosed within its own set of tags. Here's the structure:
<actual_tool_name>
<parameter1_name>value1</parameter1_name>
<parameter2_name>value2</parameter2_name>
...
</actual_tool_name>
For example, to use the attempt_completion tool:
<attempt_completion>
<result>
I have completed the task...
</result>
</attempt_completion>
Always use the actual tool name as the XML tag name for proper parsing and execution.
</error>
<environment_details>
# VSCode Visible Files
# VSCode Open Tabs
# Current Time
Current time in ISO 8601 UTC format: 2025-11-08T05:59:21.345Z
User time zone: Asia/Calcutta, UTC+5:30
# Current Cost
$0.00
# Current Mode
<slug>code</slug>
<name>💻 Code</name>
<model>moonshotai/kimi-k2-instruct-0905</model>
You have not created a todo list yet. Create one with `update_todo_list` if your task is complicated or involves multiple steps.
</environment_details>
---
**Assistant:**
<apply_diff>
<args>
<file>
<path>langchain-middleware-examples.md</path>
</file>
<diff>
<content>
<<<<<<< SEARCH
### Decorator-based Middleware (Simple Hooks)
import { createAgent, beforeModel, afterModel, wrapModelCall } from "langchain";
// Node-style: logging before model calls
@beforeModel
const logBeforeModel = (state, runtime) => {
console.log(`About to call model with ${state.messages.length} messages`);
return null; // Return null to continue normally
};
// Node-style: validation after model calls
@afterModel
const validateOutput = (state, runtime) => {
const lastMessage = state.messages[state.messages.length - 1];
if (typeof lastMessage.content === 'string' && lastMessage.content.includes("BLOCKED")) {
return {
messages: [...state.messages, { role: "assistant", content: "I cannot respond to that request." }]
};
}
return null; // Return null to continue normally
};
// Wrap-style: retry logic
@wrapModelCall
const retryModel = (request, handler) => {
for (let attempt = 0; attempt < 3; attempt++) {
try {
return handler(request);
} catch (e) {
if (attempt === 2) throw e;
console.log(`Retry ${attempt + 1}/3 after error: ${e}`);
}
}
};
const agent = createAgent({
model: "gpt-4o",
tools: [webSearch, calculator],
middleware: [logBeforeModel, validateOutput, retryModel],
});
=======
### Simple Function-based Middleware
import { createAgent, beforeModel, afterModel, wrapModelCall } from "langchain";
// Node-style: logging before model calls
const logBeforeModel = beforeModel((state, runtime) => {
console.log(`About to call model with ${state.messages.length} messages`);
return null; // Return null to continue normally
});
// Node-style: validation after model calls
const validateOutput = afterModel((state, runtime) => {
const lastMessage = state.messages[state.messages.length - 1];
if (typeof lastMessage.content === 'string' && lastMessage.content.includes("BLOCKED")) {
return {
messages: [...state.messages, { role: "assistant", content: "I cannot respond to that request." }]
};
}
return null; // Return null to continue normally
});
// Wrap-style: retry logic
const retryModel = wrapModelCall((request, handler) => {
for (let attempt = 0; attempt < 3; attempt++) {
try {
return handler(request);
} catch (e) {
if (attempt === 2) throw e;
console.log(`Retry ${attempt + 1}/3 after error: ${e}`);
}
}
});
const agent = createAgent({
model: "gpt-4o",
tools: [webSearch, calculator],
middleware: [logBeforeModel, validateOutput, retryModel],
});
>>>>>>> REPLACE
</content>
</diff>
</apply_diff>
---
**User:**
[apply_diff for 'langchain-middleware-examples.md'] Result:
The tool execution failed with the following error:
<error>
Missing value for required parameter 'args (must contain at least one valid file element)'. Please retry with complete response.
# Reminder: Instructions for Tool Use
Tool uses are formatted using XML-style tags. The tool name itself becomes the XML tag name. Each parameter is enclosed within its own set of tags. Here's the structure:
<actual_tool_name>
<parameter1_name>value1</parameter1_name>
<parameter2_name>value2</parameter2_name>
...
</actual_tool_name>
For example, to use the attempt_completion tool:
<attempt_completion>
<result>
I have completed the task...
</result>
</attempt_completion>
Always use the actual tool name as the XML tag name for proper parsing and execution.
</error>
<environment_details>
# VSCode Visible Files
# VSCode Open Tabs
# Current Time
Current time in ISO 8601 UTC format: 2025-11-08T05:59:47.706Z
User time zone: Asia/Calcutta, UTC+5:30
# Current Cost
$0.00
# Current Mode
<slug>code</slug>
<name>💻 Code</name>
<model>moonshotai/kimi-k2-instruct-0905</model>
You have not created a todo list yet. Create one with `update_todo_list` if your task is complicated or involves multiple steps.
</environment_details>
---
**Assistant:**
Let me fix the decorator syntax issue in the LangChain middleware documentation:
<apply_diff>
<args>
<file>
<path>langchain-middleware-examples.md</path>
</file>
<diff>
<content><![CDATA[
<<<<<<< SEARCH
### Decorator-based Middleware (Simple Hooks)
import { createAgent, beforeModel, afterModel, wrapModelCall } from "langchain";
// Node-style: logging before model calls
@beforeModel
const logBeforeModel = (state, runtime) => {
console.log(`About to call model with ${state.messages.length} messages`);
return null; // Return null to continue normally
};
// Node-style: validation after model calls
@afterModel
const validateOutput = (state, runtime) => {
const lastMessage = state.messages[state.messages.length - 1];
if (typeof lastMessage.content === 'string' && lastMessage.content.includes("BLOCKED")) {
return {
messages: [...state.messages, { role: "assistant", content: "I cannot respond to that request." }]
};
}
return null; // Return null to continue normally
};
// Wrap-style: retry logic
@wrapModelCall
const retryModel = (request, handler) => {
for (let attempt = 0; attempt < 3; attempt++) {
try {
return handler(request);
} catch (e) {
if (attempt === 2) throw e;
console.log(`Retry ${attempt + 1}/3 after error: ${e}`);
}
}
};
const agent = createAgent({
model: "gpt-4o",
tools: [webSearch, calculator],
middleware: [logBeforeModel, validateOutput, retryModel],
});
=======
### Simple Function-based Middleware
import { createAgent, beforeModel, afterModel, wrapModelCall } from "langchain";
// Node-style: logging before model calls
const logBeforeModel = beforeModel((state, runtime) => {
console.log(`About to call model with ${state.messages.length} messages`);
return null; // Return null to continue normally
});
// Node-style: validation after model calls
const validateOutput = afterModel((state, runtime) => {
const lastMessage = state.messages[state.messages.length - 1];
if (typeof lastMessage.content === 'string' && lastMessage.content.includes("BLOCKED")) {
return {
messages: [...state.messages, { role: "assistant", content: "I cannot respond to that request." }]
};
}
return null; // Return null to continue normally
});
// Wrap-style: retry logic
const retryModel = wrapModelCall((request, handler) => {
for (let attempt = 0; attempt < 3; attempt++) {
try {
return handler(request);
} catch (e) {
if (attempt === 2) throw e;
console.log(`Retry ${attempt + 1}/3 after error: ${e}`);
}
}
});
const agent = createAgent({
model: "gpt-4o",
tools: [webSearch, calculator],
middleware: [logBeforeModel, validateOutput, retryModel],
});
>>>>>>> REPLACE]]>
</content>
</diff>
</apply_diff>
---
**User:**
[apply_diff for 'langchain-middleware-examples.md'] Result:
The tool execution failed with the following error:
<error>
Missing value for required parameter 'args (must contain at least one valid file element)'. Please retry with complete response.
# Reminder: Instructions for Tool Use
Tool uses are formatted using XML-style tags. The tool name itself becomes the XML tag name. Each parameter is enclosed within its own set of tags. Here's the structure:
<actual_tool_name>
<parameter1_name>value1</parameter1_name>
<parameter2_name>value2</parameter2_name>
...
</actual_tool_name>
For example, to use the attempt_completion tool:
<attempt_completion>
<result>
I have completed the task...
</result>
</attempt_completion>
Always use the actual tool name as the XML tag name for proper parsing and execution.
</error>
<environment_details>
# VSCode Visible Files
# VSCode Open Tabs
# Current Time
Current time in ISO 8601 UTC format: 2025-11-08T06:00:24.720Z
User time zone: Asia/Calcutta, UTC+5:30
# Current Cost
$0.00
# Current Mode
<slug>code</slug>
<name>💻 Code</name>
<model>moonshotai/kimi-k2-instruct-0905</model>
You have not created a todo list yet. Create one with `update_todo_list` if your task is complicated or involves multiple steps.
</environment_details>