Using the Azure Function return value

This article explains how return values work inside a function. In languages that have a return value, you can bind a function output binding to the return value.

Set the name property in function.json to $return. If there are multiple output bindings, use the return value for only one of them.

How return values are used depends on the C# mode you're using in your function app:

Isolated worker model

See Output bindings in the .NET worker guide for details and examples.

In-process model

Important

Support will end for the in-process model on November 10, 2026. We highly recommend that you migrate your apps to the isolated worker model for full support.

In a C# class library, apply the output binding attribute to the method return value. In C# and C# script, alternative ways to send data to an output binding are out parameters and collector objects.

Here's C# code that uses the return value for an output binding, followed by an async example:

[FunctionName("QueueTrigger")]
[return: Blob("output-container/{id}")]
public static string Run([QueueTrigger("inputqueue")]WorkItem input, ILogger log)
{
    string json = string.Format("{{ \"id\": \"{0}\" }}", input.Id);
    log.LogInformation($"C# script processed queue message. Item={json}");
    return json;
}

[FunctionName("QueueTrigger")]
[return: Blob("output-container/{id}")]
public static Task<string> Run([QueueTrigger("inputqueue")]WorkItem input, ILogger log)
{
    string json = string.Format("{{ \"id\": \"{0}\" }}", input.Id);
    log.LogInformation($"C# script processed queue message. Item={json}");
    return Task.FromResult(json);
}

Here's the output binding in the function.json file:

{
    "name": "$return",
    "type": "blob",
    "direction": "out",
    "path": "output-container/{id}"
}

Here's the JavaScript code:

module.exports = function (context, input) {
    var json = JSON.stringify(input);
    context.log('Node.js script processed queue message', json);
    return json;
}

Here's the output binding in the function.json file:

{
    "name": "Response",
    "type": "blob",
    "direction": "out",
    "path": "output-container/{blobname}"
}

Here's the PowerShell code that uses the return value for an http output binding:

Push-OutputBinding -Name Response -Value ([HttpResponseContext]@{
    StatusCode = [HttpStatusCode]::OK
    Body = $blobname
    })

Here's the output binding in the function.json file:

{
    "name": "$return",
    "type": "blob",
    "direction": "out",
    "path": "output-container/{id}"
}

Here's the Python code:

def main(input: azure.functions.InputStream) -> str:
    return json.dumps({
        'name': input.name,
        'length': input.length,
        'content': input.read().decode('utf-8')
    })

Apply the output binding annotation to the function method. If there are multiple output bindings, use the return value for only one of them.

Here's Java code that uses the return value for an output binding:

@FunctionName("QueueTrigger")
@StorageAccount("AzureWebJobsStorage")
@BlobOutput(name = "output", path = "output-container/{id}")
public static String run(
  @QueueTrigger(name = "input", queueName = "inputqueue") WorkItem input,
  final ExecutionContext context
) {
  String json = String.format("{ \"id\": \"%s\" }", input.id);
  context.getLogger().info("Java processed queue message. Item=" + json);
  return json;
}

Next steps

Handle Azure Functions binding errors