'Tried to Use Tool Without Required Parameter': Why Cline and Roo Code Tool Calls Fail

"Cline tried to use write_to_file without value for required parameter 'content'. Retrying..." means the model sent a tool call with a required argument missing, and Cline caught it before running the tool. Roo Code shows the same message with "Roo" in place of "Cline". In most reported cases the model did not simply forget the argument: its response was cut off by an output token limit, or a provider integration dropped the arguments in transit. The fixes are to update the extension, raise the output limit, and write large files in smaller pieces. The broader lesson is the check itself. Both tools validate their own tool calls before running them, while most external API calls an agent makes get no such check.

This article covers what the error means, the documented causes, what each retry costs, how to stop the loop, and how to give external API calls the same check before they run. Checked against public Cline and Roo Code GitHub issues and documentation in October 2026.

What does "without value for required parameter" mean?

Cline and Roo Code define each built-in tool with required parameters. write_to_file needs a path and content, execute_command needs a command, and attempt_completion needs a result. When a tool call arrives without one, the extension shows the error, sends a tool error back to the model, and asks it to try again. Variants reported on GitHub include:

• Cline tried to use write_to_file without value for required parameter 'content'.
• Cline tried to use read_file without value for required parameter 'path'.
• Cline tried to use execute_command without value for required parameter 'command'.
• Cline tried to use attempt_completion without value for required parameter 'result'.
• Roo tried to use write_to_file without value for required parameter 'content'.

Both extensions give up after repeated failures. Roo Code counts consecutive mistakes and asks for your guidance after three by default, and Cline users describe the same pattern of three attempts before the task stops.

What causes it

Documented cases

• Cline issue #7998. write_to_file failed repeatedly, yet the same code came through fine when the reporter asked Cline to paste it in chat. A maintainer later traced the root cause to max_tokens being stuck at 8,192 for Claude models and said it was fixed in 3.68.0 and later.
• Cline issue #7931 (December 2025). With the Claude Code provider, read_file, list_files, execute_command, and attempt_completion all failed with missing parameters. The cause was a parsing mismatch in the provider integration, fixed by PR #8023.
• Cline PR #9276. Changed the retry message. The old message told the model to "retry with complete response", which it took literally, repeating the same oversized write until it gave up. The new message explains the likely cause and suggests a different approach.
• Roo Code issue #11795 (February 2026). The same error on Roo Code 3.50.5 through an OpenAI-compatible proxy. The analysis noted that the generic retry message gave no hint that the file was too large, so the model often repeated the same call. PR #11796 made the message actionable.

What each retry costs

A retry is another full model request. The conversation is sent again and the model generates the tool call again. Many of these failures were reported at high context usage, around 90,000 tokens in one Cline thread. At that size, three retries resend roughly 270,000 input tokens before the task stops, less whatever prompt caching saves. Because the cause is usually the same each time, identical retries tend to fail identically.

The fix that helped in both projects was a better error message. When the error names the likely cause and suggests a different action, the model changes what it does instead of repeating itself.

How to stop the loop

1. Update the extension. Cline 3.68.0 and later send a realistic max_tokens for Claude models, and recent Roo Code releases return clearer retry messages.
2. Check the output limit. Set max output tokens for your provider, and check the default on any proxy or OpenAI-compatible endpoint in between.
3. Write large files in pieces. Ask for a skeleton first, then fill it in with replace_in_file or apply_diff edits.
4. Compact the context. Use auto compact or start a new task before large writes.
5. Make it a rule. Put the incremental-write instruction in .clinerules or .roo/rules/ so you never have to repeat it.
6. Suspect the provider when every tool fails. If even read_file and list_files fail, the provider integration or a proxy is the likely culprit. Try the provider's direct API.

# .clinerules/tool-calls.md (or .roo/rules/tool-calls.md)

- Never write more than about 300 lines in one write_to_file call.
  Create a skeleton first, then add sections with replace_in_file or apply_diff.
- If a tool call fails with a missing required parameter, change the approach
  (smaller write, different tool) instead of repeating the same call.
- For third-party APIs, use the Swytchcode MCP tools: swytchcode_discover,
  then swytchcode_info, then swytchcode_exec. Never write an endpoint from memory.

The same check, applied to external API calls

Cline's error is a small example of a good design: the tool definition says what is required, and the client refuses to run a call that does not match. Built-in tools get this check. Most external API calls do not. When an agent writes a fetch call or runs curl against a provider, a missing or invented field goes straight to the provider, and the agent learns about it from an error response, or never learns at all if the provider ignores unknown fields.

Swytchcode applies that check to external APIs. Cline or Roo Code calls the Swytchcode MCP server, which resolves the operation from its catalog, validates inputs against the provider's schema, evaluates policies, resolves credentials, executes, and normalizes the response. Credentials never pass through the model's context. Errors come back with a category and a retryable flag, which gives the model what Cline's improved retry message gives it: a reason, and a signal about whether trying again makes sense.

swy init has no editor option for Cline or Roo Code, so add the MCP entry by hand. In Cline, open MCP Servers, then Configure MCP Servers. In Roo Code, use Edit Project MCP to create .roo/mcp.json, which you can commit for the team.

# Install the CLI and initialize the project
npm install -g swytchcode
swy init --mode=sandbox
swy doctor

# The loop the agent follows for any third-party call
swy discover "send a message to a Slack channel" --json
swy get <project>
swy add <canonical_id>
swy info <canonical_id>
swy exec <canonical_id>

// Cline: MCP settings (Configure MCP Servers)
{
  "mcpServers": {
    "swytchcode": {
      "command": "swytchcode",
      "args": ["mcp", "serve"],
      "disabled": false,
      "autoApprove": ["swytchcode_discover", "swytchcode_info", "swytchcode_list"]
    }
  }
}

// Roo Code: .roo/mcp.json
{
  "mcpServers": {
    "swytchcode": {
      "command": "swytchcode",
      "args": ["mcp", "serve"],
      "alwaysAllow": ["swytchcode_discover", "swytchcode_info", "swytchcode_list"]
    }
  }
}

Lookups are auto-approved and swytchcode_exec is left off the list, so every live call still asks you first. In Roo Code, per-tool auto-approval also requires the global "Use MCP servers" auto-approve setting.

What happens when an external call is wrong:

• Unknown or not-enabled operations are rejected. An invented canonical ID, or a real one that has not been added to the project, exits with code 2 and no request is sent.
• Missing or invented fields fail validation. A missing required field, a wrong type, or a field the schema does not define exits with code 1 before the provider sees the request.
• Provider errors come back structured. Each error includes the status code, an error category, and whether it is retryable. A 200 response with an error in the body counts as a failure.
• Writes can be held. dry_run=true previews the request without sending it. For production, allow and deny rules are available from the Pro plan, and approval rules that route a call to Slack or Telegram are available on Business and Enterprise.

Where this does not help

Swytchcode does not fix Cline's or Roo Code's own tool calls. A write_to_file that loses its content to an output limit is solved by the steps above, and no execution layer can stop a response from being cut off partway through. What Swytchcode adds is the guarantee that an external API call matches the real schema before it is sent. It also cannot tell whether a valid value is the right one for your task, so keep approvals on writes.

Frequently asked questions

Why does Cline say "tried to use write_to_file without value for required parameter 'content'"?
The model's tool call arrived without the file content, almost always because the response hit an output token limit during a large write. Update to Cline 3.68.0 or later, raise the output limit, and write large files in smaller pieces.

Is the Roo Code error the same problem?
Yes. Roo Code shows the same message with "Roo" in place of "Cline", and the documented causes match: output truncation, proxies with low token limits, and occasional parser bugs.

Why does Cline retry the same failing call?
Older retry messages only said the parameter was missing, so the model repeated the call. Cline PR #9276 and Roo Code PR #11796 changed the messages to explain the likely cause and suggest a different approach.

How many times does Roo Code retry?
Roo Code's consecutive mistake limit defaults to three. After that it stops and asks for your guidance.

Can Cline and Roo Code use Swytchcode?
Yes, through MCP. Add a swytchcode server with command swytchcode and args mcp serve in Cline's MCP settings or in Roo Code's .roo/mcp.json.

Swytchcode resources

• Why AI agents call the wrong API: https://www.swytchcode.com/content/why-your-ai-agent-calls-the-wrong-api-and-how-to-fix-it
• Why Claude Code guesses API endpoints: https://www.swytchcode.com/content/why-claude-code-guesses-api-endpoints
• Why Codex calls the wrong API: https://www.swytchcode.com/content/codex-wrong-api-calls
• Windsurf Cascade calls APIs that don't exist: https://www.swytchcode.com/content/windsurf-cascade-wrong-api-endpoints
• Swytchcode MCP server docs: https://docs.swytchcode.com/cli/mcp/
• CLI command reference: https://docs.swytchcode.com/reference/commands/
• Supported APIs: https://www.swytchcode.com/apis