This guide describes how you can monitor and debug your functions in production. ## How it works Functions can fail by raising an exception, exceeding memory or time limits, or returning data that doesn't match the schema of the specific [Function API](/docs/api/functions). In other cases, the function can run successfully, but return unexpected results due to a bug in the function code. To aid in debugging issues with a function, information about each function run is stored and made available through the [Partner Dashboard](https://partners.shopify.com/current/apps). This includes metadata, such as when the run occurred and the shop that it was on, and function run details such as the function input and output. Function run details are hidden by default for production shops because they can contain Personally Identifying Information (PII), unless they're shared by merchants. Merchants can share function run details by sharing an error report when the function fails or by sharing all function logs for an app. Development shops are an exception and have all function run details visible. ## Sharing function run details When a merchant shares function run details from the Shopify admin, you can access them from the app's **Extensions** section in your [Partner Dashboard](https://partners.shopify.com/current/apps). ### Sharing an error report When a function is executed and an error occurs, a warning notification is displayed on the relevant page in the Shopify admin. For example, if you've executed a discount function, then the warning notification appears on the **Discounts** page. The warning notification contains information about when errors started occurring. It also includes a link that enables users to share information with developers about function runs that failed. 1. From the Shopify admin, navigate to the page that's associated with the executed function. 1. Click the warning notification. 1. Click **Share the error reports with ``**. 1. Choose whether to include every time the customization ran within the last 24 hours. 1. Click **Share**. An email notification is sent to the Partner organization's specified business contact. > Note: > Sharing the last 24 hours of runs includes successful executions. ### Share app function logs Merchants can share all function run details for an app within the past 24 hours, whether there were function failures or not. 1. From the Shopify admin, navigate to the **Apps and sales channels** settings. 1. Select the app that you need to share function run details for. 1. Click the **Share logs** button in the **Share function logs** card. 1. Click the **Share logs** button in the modal. An email notification is sent to the Partner organization's specified business contact. ## Debug a function You can debug your function from the app's **Extensions** section in your [Partner Dashboard](https://partners.shopify.com/current/apps). 1. From your Partner Dashboard, go to **Apps**. 1. Click the app that you deployed your function to. 1. Click **Extensions**. 1. Click the name of your function. The function details page contains a list of function runs. After the merchant has consented to share function run details, you can inspect the details of each individual function run. > Note: > Functions are deterministic, which means that any time they execute with a given input, they always return the same output. You can therefore copy the input in a function run and accurately reproduce the failing execution locally using [Shopify CLI](/docs/apps/build/functions/test-debug-functions#execute-the-function-locally-using-shopify-cli) or a [unit test](/docs/apps/build/functions/test-debug-functions#writing-unit-tests-for-functions).  1. **Input (`STDIN`)**: The JSON formatted input that you can copy to your clipboard. For illustrative purposes, the input in the screenshot has been omitted. 2. **Output (`STDOUT`)**: Contains the output, if the function returned output 3. **Logs (`STDERR`)**: Contains the `STDERR` logs of the function 4. **Error message**: Contains the final message sent to `STDERR` before the function failed > Caution: > Function logs to `STDERR` are truncated after 1 kB. Some Wasm toolchains might crash if `STDERR` fails to write full logs. ## List of errors The following table provides a complete list of errors that can occur when running your function: | Error name | Description | |---|---| | `TimeoutError` | Shopify stopped the function after it ran for over 10 milliseconds (ms). | | `RunError` | The function raised an exception. | | `InstructionCountLimitExceededError` | Shopify stopped the function after it exceeded the maximum instruction count of 11 million instructions. | | `StackMemoryLimitExceededError` | Shopify stopped the function after it exceeded the maximum stack size of 512kb. | | `LinearMemoryLimitExceededError` | Shopify stopped the function after it exceeded the maximum linear memory size of 10mb. | | `InvalidOutputError` | The function returned malformed or invalid output. This might occur because you printed debugging information to `STDOUT`, which is reserved for function output. If that's the case, then use `STDERR` instead. | | `UnsupportedError` | The generated Wasm doesn't conform to [Shopify Functions standards](/docs/apps/build/functions/programming-languages/webassembly-for-functions). | | `InvalidVariableValueError` | The function's input query variables metafield was invalid. This can occur if the metafield value doesn't conform to the variables definitions, or if the metafield type isn't `json`. For more information, refer to [using variables in input queries](/docs/apps/build/functions/input-output/use-variables-input-queries). |