But with all its speed and power comes a challenge—observability and testing. Unlike RESTful APIs, gRPC traffic isn't human-readable, making debugging, testing, and traffic inspection more difficult. In this blog, we’ll explore why and how to capture gRPC traffic, what tools you can use, and how it helps in improving the overall quality of your system.
Why Capture gRPC Traffic?
Capturing gRPC traffic is essential for several reasons:
1. Debugging Issues
When something goes wrong in your system, logs can only take you so far. Capturing gRPC traffic helps you understand what data was sent and received, especially when tracking down hard-to-reproduce bugs.
2. API Testing
Capturing real gRPC traffic allows you to build test cases based on real usage. This is more effective than manually crafting test data and helps catch edge cases you might miss.
- Performance Analysis
You can analyze captured traffic to measure payload size, latency, and call frequency. This helps optimize performance and reduce bottlenecks.
4. Dependency Mocking
With captured traffic, you can mock dependent services for integration testing. This ensures stable tests even when external systems are down or unavailable.
Challenges in Capturing gRPC Traffic
Unlike REST APIs, which use plain-text HTTP requests, gRPC uses Protocol Buffers (Protobuf) for serialization and HTTP/2 for transport. This means:
- You can't just open a terminal and inspect traffic with curl.
- Traffic is binary and compressed.
- Bi-directional streaming makes it harder to trace request/response pairs.
To effectively capture gRPC traffic, you need tools that understand gRPC’s encoding and transport mechanisms.
Tools to Capture gRPC Traffic
Here are some popular tools and approaches you can use to capture gRPC calls for debugging, logging, or testing.
- Keploy
Keploy is an open-source testing tool that can capture gRPC traffic and automatically convert it into test cases and mocks. It listens to real API traffic—including gRPC—and uses it to build high-coverage test suites.
???? Key Features:
- Captures real gRPC traffic from running applications
- Auto-generates test cases with inputs and outputs
- Mocks dependencies (DB, gRPC, HTTP)
- Integrates easily with CI/CD pipelines
Use Case: If you want to test gRPC APIs without writing a single test manually, Keploy is your go-to tool.
- Wireshark
Wireshark is a well-known network protocol analyzer that can capture low-level network traffic, including HTTP/2. It allows you to inspect raw gRPC packets.
???? Key Features:
- Deep packet inspection
- Can decode HTTP/2 traffic
- Supports TLS decryption (with some effort)
Limitations: Interpreting gRPC messages requires the .proto file to decode the binary Protobuf data.
- grpc-dump
grpc-dump is a lightweight tool that allows you to intercept and dump gRPC traffic between clients and servers.
???? Key Features:
- Acts as a proxy between client and server
- Dumps Protobuf messages
- Supports TLS
Use Case: Great for developers who want to inspect gRPC calls during development without diving into network sniffers.
- gRPC Interceptors
If you're building or maintaining the gRPC service yourself, you can add custom interceptors to log or capture traffic at the server or client level.
???? Key Features:
- Code-level access to gRPC requests and responses
- Custom logic for logging, auditing, or test generation
Drawback: Requires code changes and recompilation.
How Capturing gRPC Traffic Enhances Testing
By capturing gRPC traffic, you can go beyond unit testing and simulate real-world scenarios. Tools like Keploy let you:
- Generate test cases directly from real traffic
- Detect regressions when changes affect gRPC contract behavior
- Create mocks for dependent services, allowing tests to run in isolation
This leads to:
- Higher confidence in deployments
- Faster feedback loops
- Fewer bugs in production
Capture Once, Test Forever
Instead of spending hours crafting test payloads, you can now capture gRPC traffic once and replay it anytime you want to test or validate your system. This strategy is especially useful for:
- CI/CD pipelines
- Regression testing
- Integration with third-party services
Conclusion: Visibility Is Power
Capturing gRPC traffic might seem like a low-level detail, but it opens the door to smarter debugging, automated testing, and improved software quality. With modern tools like Keploy, developers no longer have to choose between speed and reliability.
If you’re building or maintaining gRPC-based services, make capturing traffic part of your regular development and testing workflow. It’s the key to ensuring that your services behave as expected—under real-world conditions.
???? Get started with Keploy:
https://keploy.io