Troubleshooting Xcodebuild MCP Timeout Errors

If you're encountering consistent timeout errors with the build_sim tool in Xcodebuild MCP (Machine Control Protocol), you're not alone. This issue, characterized by the error message "MCP error -32001: Request timed out," can be puzzling and frustrating. This comprehensive guide delves into the potential causes of this problem and provides actionable steps to troubleshoot and resolve it. Whether you're working on agentic loops or specific repros in KiloCode, understanding the intricacies of Xcodebuild MCP is crucial. We'll explore the error's context, analyze potential culprits such as full paths, and offer insights into debugging strategies. By the end of this article, you'll have a clearer understanding of how to tackle this issue and ensure smooth build simulations.

This article aims to provide a comprehensive guide to diagnosing and resolving the frustrating "MCP error -32001: Request timed out" issue specifically encountered when using the build_sim tool within Xcodebuild MCP (Machine Control Protocol). This error frequently occurs during agentic loops or when generating specific repros in environments like KiloCode. Understanding the nuances of this error is critical for developers aiming to streamline their Xcode build processes and leverage LLMs (Large Language Models) for automated tasks. This article will explore the context of the error, potential root causes, and systematic troubleshooting steps to help you efficiently resolve this problem and maintain a productive development workflow. Let's dive into the details to equip you with the knowledge and tools necessary to tackle this challenge head-on.

The primary issue at hand is the consistent failure of the build_sim tool within Xcodebuild MCP, manifesting as an "MCP error -32001: Request timed out." This error typically arises when the LLM sends arguments to the tool, such as project paths, schemes, and simulator names. For instance, an LLM like Opus 4.5 or Sonnet 4.5 might provide arguments like this:

{
 "projectPath": "/Users/adamhill/dev/apple/TheElectricSlideV3/sources/TheElectricSlide/TheElectricSlide.xcodeproj",
 "scheme": "TheElectricSlide",
 "simulatorName": "iPhone 16"
}

However, instead of a successful build, the process terminates with the timeout error. Interestingly, when Xcodebuild is executed directly from the command line, it often succeeds, adding another layer of complexity to the problem. This discrepancy suggests that the issue might be specific to how Xcodebuild MCP handles certain build requests, particularly those involving simulator builds. The error's consistency across different SOTA models, including Opus 4.5, Sonnet 4.5, and even GPT 5.1, indicates a systemic problem rather than a model-specific quirk. Addressing this error is crucial for ensuring the reliability of automated build processes and maintaining efficient development workflows.

This error message, “MCP error -32001: Request timed out,” indicates that the Xcodebuild MCP tool is unable to complete the build_sim task within the allotted time. This can be a particularly vexing issue because while the automated system using MCP fails, manual execution via the command line often succeeds. This discrepancy suggests that the problem lies not within the Xcode build process itself, but rather in how MCP interfaces with Xcodebuild. One key aspect to consider is the context in which the command is executed. When an LLM triggers the build_sim tool, it may not have the same environmental context as a direct command-line invocation. This lack of context can lead to various issues, such as incorrect paths, missing environment variables, or other configuration discrepancies. Therefore, understanding the specific environment in which MCP operates is crucial for diagnosing and resolving this timeout error. Let’s delve deeper into potential causes and solutions in the following sections.

Several factors could contribute to the timeout error. One initial thought is the use of a full path for the project file. While seemingly straightforward, providing the full path might introduce complications within the MCP's execution environment. It's essential to consider whether the MCP tool correctly interprets and handles absolute paths. Another possibility lies in the environment variables and configurations that Xcodebuild MCP relies on. If certain environment variables are not correctly set or if the configuration is not aligned with the project's requirements, it could lead to timeouts. Additionally, resource constraints or performance issues on the machine running the build could also be factors. If the system is under heavy load or lacks sufficient resources, the build process might take longer than the allotted time, resulting in a timeout error. Furthermore, the complexity of the project itself can play a role. Large projects with numerous dependencies and intricate build configurations might require more time to build, potentially exceeding the MCP's timeout limit. To effectively troubleshoot, each of these potential causes must be systematically investigated.

The investigation into the timeout error reveals several potential causes that need careful examination. One of the primary suspects is the use of full paths in the arguments passed to the build_sim tool. While providing the full path seems like a straightforward way to ensure the tool knows exactly where to find the project, it can sometimes lead to issues within the MCP environment. The MCP might not handle absolute paths as expected, or there could be discrepancies in how paths are resolved compared to direct command-line execution. Another critical area to explore is the environmental context in which MCP operates. Unlike a command-line build, where the environment is explicitly set up, MCP runs within its own managed environment, which might be missing certain variables or configurations required for a successful build. This includes not only environment variables but also potential differences in the current working directory or other runtime settings. Additionally, it's important to consider the resource constraints and system load on the machine running the build. If the system is under heavy load, the build process might take longer, leading to timeouts. Finally, the complexity of the Xcode project itself can be a factor. A large project with many dependencies, complex build configurations, and extensive codebases can naturally take longer to build, making it more susceptible to timeout errors. A methodical approach to diagnosing these factors will help pinpoint the root cause of the issue.

To effectively debug this issue, a systematic approach is crucial. Start by examining the XcodeBuildMCP Doctor output. This diagnostic tool provides a wealth of information about the system environment, Xcode configuration, and available tools. Pay close attention to any warnings or errors, particularly those related to missing dependencies or misconfigurations. Next, scrutinize the MCP configuration itself, especially the alwaysAllow list. Ensure that all necessary tools and workflows are included and that there are no restrictive settings that might be causing the timeout. Experimenting with different path configurations can also be insightful. Try using relative paths instead of full paths to see if that resolves the issue. Monitoring system resources during the build process is another essential step. Keep an eye on CPU usage, memory consumption, and disk I/O to identify any bottlenecks that might be contributing to the timeout. Furthermore, logging and tracing MCP's execution can provide valuable clues. By enabling verbose logging, you can gain insights into the tool's internal operations and pinpoint exactly where the timeout occurs. Finally, consider simplifying the build process for testing purposes. Try building a smaller, less complex project to see if the issue persists. If the simplified build succeeds, it suggests that the problem might be related to the complexity of the original project.

Debugging this type of issue requires a methodical and multi-faceted approach. One of the first steps should be to examine the output from the XcodeBuildMCP Doctor tool. This diagnostic tool provides a comprehensive overview of the system's configuration, Xcode environment, and any potential issues. Key areas to focus on include missing dependencies, incorrect paths, and warnings related to the Xcode installation or environment variables. Next, it's crucial to review the MCP configuration itself. Pay close attention to settings such as the alwaysAllow list, which specifies the tools and commands that MCP is permitted to execute. Ensure that all necessary build tools and workflows are included, and that there are no unintended restrictions that might be causing the timeout. Another valuable technique is to experiment with different path configurations. Try using relative paths instead of absolute paths for the project file to see if this resolves the issue. This can help determine if the problem lies in how MCP handles full paths versus relative paths. Monitoring system resources during the build process is also essential. Use tools to track CPU usage, memory consumption, and disk I/O to identify any bottlenecks or resource constraints that might be contributing to the timeout. If the system is under heavy load, it could be slowing down the build process and causing it to exceed the timeout limit. Additionally, consider implementing verbose logging within MCP to gain more insight into its internal operations. Detailed logs can help pinpoint exactly where the timeout occurs and provide clues about the underlying cause. Finally, a useful strategy is to simplify the build process as much as possible for testing purposes. Try building a smaller, less complex project to see if the issue persists. If a simplified build succeeds, it suggests that the problem might be related to the complexity or configuration of the original project. By systematically working through these debugging steps, you can narrow down the root cause of the timeout error and implement an effective solution.

The XcodeBuildMCP Doctor tool provides a comprehensive report that can be invaluable for diagnosing issues. The "System Information" section offers insights into the platform, OS release, architecture, CPU, memory, hostname, username, and directories. This information helps ensure that the environment meets the minimum requirements for Xcodebuild and MCP. The "Node.js Information" section is crucial for verifying the Node.js version and execution path, as Xcodebuild MCP relies on Node.js. The "Xcode Information" section details the Xcode version, path, and selected Xcode, which is essential for confirming that the correct Xcode version is being used. The "Dependencies" section lists the status of various dependencies like axe and xcodemake. Missing dependencies can often lead to build failures, so it's important to ensure that all required dependencies are installed and correctly configured. The "Environment Variables" section displays the values of various environment variables, which can impact the build process. Pay close attention to variables like INCREMENTAL_BUILDS_ENABLED and DEVELOPER_DIR, as they can affect build behavior. The "PATH" variable lists the directories that the system searches for executables, and it's important to ensure that the necessary tools are included in the PATH. The "Feature Status" section provides an overview of available features, such as UI Automation, Incremental Builds, and Mise Integration. If certain features are not available, it might indicate a configuration issue. The "Tool Availability Summary" gives a quick overview of the availability of different tool categories, such as Build Tools and UI Automation Tools. Finally, the "Sentry" section indicates whether Sentry error tracking is enabled, which can be helpful for identifying and addressing issues. By carefully analyzing each section of the XcodeBuildMCP Doctor output, you can gain a holistic view of the system and identify potential problem areas.

Analyzing the output from the XcodeBuildMCP Doctor tool is a crucial step in diagnosing issues. This tool provides a wealth of information about the system's configuration, Xcode environment, and available resources. Let’s break down the key sections of the output and discuss how to interpret them. The "System Information" section provides details about the operating system, hardware, and user environment. This includes the platform (e.g., Darwin), OS release, architecture (e.g., arm64), CPU specifications, memory, hostname, username, and important directories like the home directory and temporary directory. This information helps verify that the environment meets the minimum requirements for running Xcodebuild MCP and can highlight potential compatibility issues. The "Node.js Information" section is critical because Xcodebuild MCP relies on Node.js. It provides the Node.js version, execution path, process ID (PID), parent process ID (PPID), platform, architecture, current working directory (CWD), and command-line arguments. Ensuring that the correct Node.js version is installed and that the execution path is properly configured is essential for the tool to function correctly. The "Xcode Information" section details the Xcode version, path, selected Xcode, and xcrun version. This section is crucial for verifying that the tool is using the correct Xcode installation and that the necessary Xcode command-line tools (xcrun) are available. Discrepancies in these settings can lead to build failures and other issues. The "Dependencies" section lists the status of various dependencies, such as axe (for UI automation) and xcodemake (for incremental builds). Missing or misconfigured dependencies can cause significant problems, so it’s important to ensure that all required dependencies are installed and correctly set up. The "Environment Variables" section displays the values of various environment variables that can impact the build process. Key variables to review include INCREMENTAL_BUILDS_ENABLED, DEVELOPER_DIR, HOME, USER, TMPDIR, NODE_ENV, SENTRY_DISABLED, XCODEBUILDMCP_DYNAMIC_TOOLS, and XCODEBUILDMCP_SILENCE_LOGS. Incorrectly set environment variables can lead to unexpected behavior and build failures. The "PATH" variable is particularly important as it lists the directories the system searches for executables. Ensuring that necessary tools and binaries are included in the PATH is crucial for Xcodebuild MCP to function correctly. The "Feature Status" section provides an overview of available features, such as UI Automation, Incremental Builds, and Mise Integration. This section helps identify whether certain features are enabled and available, which can impact the functionality of the tool. The "Tool Availability Summary" gives a quick overview of the availability of different tool categories, including Build Tools, UI Automation Tools, and Incremental Build Support. This summary helps assess whether the necessary tools are available for the tasks you are trying to perform. Finally, the "Sentry" section indicates whether Sentry error tracking is enabled, which can be valuable for monitoring and diagnosing issues. By thoroughly analyzing each section of the XcodeBuildMCP Doctor output, you can gain a comprehensive understanding of the system's configuration and identify potential areas of concern, making it an essential tool in troubleshooting Xcodebuild MCP issues.

The MCP configuration plays a pivotal role in how Xcodebuild MCP operates. The command and args settings dictate how the tool is invoked, and any misconfiguration here can lead to failures. The env settings specify the environment variables that are set during the tool's execution, and incorrect environment variables can cause unexpected behavior. The alwaysAllow list is particularly critical, as it defines the tools and workflows that MCP is permitted to execute. If build_sim is not included in this list or if there are conflicting entries, it can result in the timeout error. Reviewing this list is essential to ensure that all necessary tools are allowed. Additionally, the configuration might include settings related to timeouts or resource limits, which could be contributing to the issue. If the timeout value is set too low or if there are overly restrictive resource limits, it can cause the build process to terminate prematurely. Understanding the intricacies of the MCP configuration is crucial for troubleshooting and resolving build failures.

Understanding the MCP (Machine Control Protocol) configuration is paramount when diagnosing issues like the timeout error. The MCP configuration file is where you define how Xcodebuild MCP operates, including the commands it can execute, the arguments it passes, and the environment in which it runs. Let's delve into the key aspects of the MCP configuration and how they can impact the build_sim tool. The `