Fix SWA Deploy Error: Missing Function Language Info

Nov 13, 2025 by Alex Johnson 53 views

Troubleshooting SWA Deploy Failures: 'Cannot deploy to the function app because Function language info isn't provided'

Encountering the frustrating error message "Cannot deploy to the function app because Function language info isn't provided" during a Static Web Apps (SWA) deployment, even after seemingly providing all the necessary apiRuntime configurations and flags, can be a real head-scratcher. This article aims to dissect this issue, exploring potential causes and offering solutions to get your SWA deployment back on track. We'll cover everything from verifying your configurations to understanding how the SWA CLI processes these settings.

Understanding the Error: Why is SWA Complaining?

The core of the problem lies in how the SWA CLI and its underlying deployment mechanisms interpret and propagate the function language information. This information is crucial because it tells Azure Functions, the serverless compute platform powering your SWA's API, which runtime environment to use (e.g., Node.js, Python, .NET). When this information is missing or incorrectly passed, the deployment process halts, resulting in the error you're seeing.

There are several potential reasons why this error might occur, even when you believe you've provided the necessary information:

Configuration Precedence: The SWA CLI can receive configuration from multiple sources: command-line flags, environment variables, and configuration files (staticwebapp.config.json and swa-cli.config.json). Understanding the order in which these sources are evaluated is critical. Flags usually take precedence over environment variables, which in turn take precedence over configuration files.
Incorrect Flag Usage: Ensure you're using the correct flags and that they are properly formatted. Typos or incorrect syntax can lead to the CLI ignoring your intended settings. Pay close attention to the --api-language and --api-version flags.
File Path Issues: The --api-location and --output-location flags tell the SWA CLI where to find your API and static assets, respectively. If these paths are incorrect, the CLI might not be able to locate your staticwebapp.config.json file or your API code, leading to missing runtime information.
CLI Version Inconsistencies: While less common, bugs in specific versions of the SWA CLI could cause misinterpretation of configuration settings. It's always a good idea to keep your CLI updated to the latest stable version.
Underlying Deployment Issues: The error message might sometimes be a symptom of a deeper problem with the Azure Functions deployment pipeline. This could involve issues with Azure's internal services, which are harder to diagnose directly.

Diagnosing and Resolving the Issue

Now that we understand the potential causes, let's move on to practical steps for diagnosing and resolving the "Cannot deploy to the function app because Function language info isn't provided" error.

1. Verify Your Configuration Sources

Start by systematically checking each of your configuration sources to ensure the API runtime information is correctly specified.

Command-Line Flags: Double-check the swa deploy command you're using. Make sure the --api-language and --api-version flags are present and have the correct values. For example:
```
swa deploy --app-name my-first-static-web-app --env production --output-location build --api-location api --api-language node --api-version 16
```
Environment Variables: If you're using environment variables, verify that FUNCTION_LANGUAGE and FUNCTION_LANGUAGE_VERSION are set correctly in your environment. Remember that these variables will be overridden if the corresponding flags are present in your swa deploy command.

macOS/Linux: export FUNCTION_LANGUAGE=node && export FUNCTION_LANGUAGE_VERSION=16

Windows: set FUNCTION_LANGUAGE=node && set FUNCTION_LANGUAGE_VERSION=16
staticwebapp.config.json: If you're using a staticwebapp.config.json file, make sure it's located in the correct output directory (specified by --output-location) and that the platform.apiRuntime property is correctly defined:
```
{
  "navigationFallback": {
    "rewrite": "/index.html"
  },
  "platform": {
    "apiRuntime": {
      "language": "node",
      "version": "16"
    }
  }
}
```
swa-cli.config.json: Check your swa-cli.config.json file for conflicting or incorrect settings related to apiLanguage and apiVersion. This file is typically used for local development and might not always be relevant for production deployments, but it's worth checking for inconsistencies.

2. Use Verbose Logging

The SWA CLI's verbose logging can provide valuable insights into the deployment process. Use the --verbose=silly flag to get the most detailed output. This will show you how the CLI is interpreting your configuration settings and any errors that occur during deployment.

swa deploy --app-name my-first-static-web-app --env production --output-location build --api-location api --api-language node --api-version 16 --verbose=silly

Examine the output carefully for any clues about why the API runtime information is not being recognized. Look for messages related to environment variable loading, configuration file parsing, and API directory detection.

3. Simplify Your Deployment Command

To isolate the issue, try simplifying your swa deploy command by removing unnecessary flags or options. For example, if you're not using environment variables or a staticwebapp.config.json file, try explicitly specifying the --api-language and --api-version flags.

4. Clear Cache and Reinstall the SWA CLI

Sometimes, cached data or corrupted installations can cause unexpected behavior. Try clearing your npm cache and reinstalling the SWA CLI:

npm cache clean --force
npm uninstall -g @azure/static-web-apps-cli
npm install -g @azure/static-web-apps-cli

5. Experiment with Different Node.js Versions

While you've specified Node.js 16, it's worth experimenting with other supported versions to see if that resolves the issue. You can try Node.js 18 or 20, for example. Make sure your local development environment also aligns with the version you are deploying to.

6. Check Azure Functions Core Tools Version

Ensure that you have the correct version of Azure Functions Core Tools installed. This is essential for local development and can sometimes impact deployment behavior. You can check your version by running func --version in your terminal.

7. Validate Your `package.json`

Make sure your api/package.json file is valid and includes the necessary dependencies, especially @azure/functions. A corrupted or incomplete package.json file can sometimes lead to deployment issues.

8. Contact Azure Support

If you've tried all the above steps and are still unable to resolve the issue, it's time to reach out to Azure support. They have access to internal logs and diagnostic tools that can help pinpoint the root cause of the problem.

When contacting support, be sure to provide the following information:

Your SWA app name
The exact swa deploy command you're using
The verbose log output
Your staticwebapp.config.json and api/package.json files
Any other relevant information about your environment and configuration

Example Scenario and Solution

Let's consider a specific scenario where the user has the following setup:

app build at: ./build (contains build/staticwebapp.config.json with platform.apiRuntime set to node:16)
api folder at: ./api (contains package.json)
Commands run: swa deploy --app-name my-first-static-web-app --env production --output-location build --api-location api --api-language node --api-version 16 --verbose=silly

Even with all these settings, the deployment fails with the "Cannot deploy to the function app because Function language info isn't provided" error.

Possible Solution:

In this case, the issue might be related to the way the SWA CLI is resolving the API location. Even though the --api-location flag is provided, the CLI might not be correctly identifying the API directory. A potential solution is to explicitly specify the full path to the API directory using the pwd command in bash:

swa deploy --app-name my-first-static-web-app --env production --output-location build --api-location "$(pwd)/api" --api-language node --api-version 16 --verbose=silly

This ensures that the CLI has the correct absolute path to the API directory, which can resolve issues with relative path resolution.

Conclusion

The "Cannot deploy to the function app because Function language info isn't provided" error can be a frustrating obstacle during SWA deployments. However, by systematically verifying your configuration sources, using verbose logging, and experimenting with different settings, you can often diagnose and resolve the issue. Remember to consult the official Azure documentation for the most up-to-date information and guidance. If all else fails, don't hesitate to reach out to Azure support for assistance. Good luck, and happy deploying!