A critical need, when creating multi-agent applications is to manage token usage in API calls. This is where middleware plays a crucial role. In this post, we will explore what middleware is within the Microsoft Agent Framework, why it is essential for capping token usage, and how to implement it effectively.

What is Middleware in the Microsoft Agent Framework?
Middleware serves as an intermediary layer that processes requests and responses between users and AI agents. It acts as a bridge, allowing developers to intercept, inspect, and modify the data flowing through the system. This capability is vital for implementing additional logic, such as validation, logging, and, importantly, token management.
In the context of the Microsoft Agent Framework, middleware can be utilized to enhance the functionality of AI agents by providing a structured way to handle requests and responses. This not only improves the overall efficiency of the system but also allows for greater control over how the AI interacts with users.
Why Use Middleware to Cap Token Usage?
1. Control Costs
One of the primary reasons to implement middleware for capping token usage is cost management. Many AI services, including those provided by Microsoft, charge based on the number of tokens processed during interactions. By using middleware to monitor and limit token usage, organizations can prevent unexpected spikes in expenses. This is particularly important for businesses that rely heavily on AI for customer service, content generation, or data analysis.
2. Enhance Security
Security is a paramount concern when dealing with AI agents, especially in environments that handle sensitive data. Middleware can validate requests before they reach the agent, ensuring that only legitimate requests are processed. This validation step is crucial for preventing malicious attacks or unintended data exposure, thereby enhancing the overall security posture of the application.
3. Improve Performance
Middleware can also play a significant role in optimizing the performance of AI agents. By intercepting and modifying requests and responses, middleware can streamline the data flow, reducing latency and improving response times. This ensures that the AI agent operates efficiently, providing users with a seamless experience.
4. Custom Logic Implementation
Another advantage of middleware is the ability to implement custom logic tailored to specific business needs. For instance, organizations can modify the input or output of the AI agent based on predefined business rules or user requirements. This flexibility allows for a more personalized interaction, enhancing user satisfaction and engagement.
Types of Middleware in the Microsoft Agent Framework
The Microsoft Agent Framework offers several types of middleware, each serving a unique purpose:
1. Agent Run Middleware
This type of middleware intercepts all agent runs, allowing developers to inspect and modify both input and output. It is particularly useful for implementing global logic that applies to all interactions with the agent.
2. Function Calling Middleware
Function calling middleware intercepts function calls made by the agent, enabling similar inspection and modification capabilities. This is beneficial for managing specific functions that may require additional validation or processing.
3. Streaming Middleware
Designed specifically for handling streaming data, streaming middleware allows for real-time modifications. This is essential for applications that require continuous data flow, such as live chatbots or real-time analytics.
Example of Middleware Implementation
To illustrate how middleware can be implemented to cap token usage, consider the following example in C#:
public class TokenUsageMiddleware
{
private readonly RequestDelegate _next;
private const int MAX_TOKENS = 1000; // Define your maximum token limit
public TokenUsageMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task InvokeAsync(HttpContext context)
{
// Inspect the incoming request
var tokenCount = CountTokens(context.Request.Body);
// Cap the token usage
if (tokenCount > MAX_TOKENS)
{
context.Response.StatusCode = StatusCodes.Status400BadRequest;
await context.Response.WriteAsync("Token limit exceeded.");
return;
}
// Call the next middleware in the pipeline
await _next(context);
}
private int CountTokens(Stream requestBody)
{
// Logic to count tokens in the request body
// This is a placeholder for actual token counting logic
return 0; // Replace with actual token counting implementation
}
}
In this example, the TokenUsageMiddleware class intercepts incoming requests, counts the tokens, and checks if the count exceeds a predefined limit. If the limit is exceeded, it returns a 400 Bad Request response, effectively capping token usage.
Additional Real-World Use Cases
Cost Management
Organizations utilizing AI services, such as OpenAI’s GPT models, can implement middleware to monitor and cap token usage. This ensures that they remain within budget and avoid unexpected costs associated with excessive API calls.
Data Validation
Middleware can also be employed to validate user inputs before they reach the AI agent. This prevents invalid or harmful requests from being processed, safeguarding the integrity of the system and enhancing user experience.
Conclusion
Middleware in the Microsoft Agent Framework is a powerful tool for managing interactions with AI agents. By implementing middleware to cap token usage, organizations can effectively control costs, enhance security, and improve performance. This makes middleware an essential component of modern AI applications, enabling businesses to leverage the full potential of AI while maintaining control over their resources.
My blog post application has been updated to cap token usage here.













