Modern developers frequently face the challenge of selecting the appropriate tools for interacting with APIs. REST APIs and gRPC APIs have emerged as dominant technologies in this space. While REST is widely used for its simplicity and ease of integration, gRPC is gaining popularity for its performance and modern design, which is suited for microservices and real-time communication.
cURL has long been the go-to command-line utility for testing and debugging RESTful APIs. Its simplicity, flexibility, and support across platforms make it a developer favorite. On the other hand, grpcurl has emerged as a powerful alternative for gRPC services, offering a familiar command-line interface tailored for gRPC communication.
This raises an essential question: Is grpcurl similar to cURL for REST APIs? This guide provides a step-by-step comparison to help developers understand where each tool fits in, its features, and how it serves its respective protocols.
What is cURL?
Definition and Purpose
cURL stands for “Client URL” and is a command-line tool used for transferring data with URLs. It supports numerous protocols, including HTTP, HTTPS, FTP, and more. cURL is widely used for testing REST APIs, making HTTP requests, uploading files, and simulating user interactions with web services.
Use Case in RESTful APIs
In REST-based environments, cURL enables developers to perform operations such as GET, POST, PUT, DELETE, and PATCH. It allows testing endpoints by sending HTTP requests directly from the terminal. cURL’s versatility, combined with its support for headers, authentication, and payloads, makes it invaluable in REST development.
What is grpcurl?
Definition and Primary Function
grpcurl is a command-line tool designed specifically for interacting with gRPC servers. Just like cURL interacts with REST APIs, grpcurl enables users to call gRPC methods, inspect available services, and send request payloads directly from the terminal. It is beneficial for testing and debugging gRPC APIs.
Use in gRPC-Based Systems
In gRPC systems, grpcurl simplifies the developer’s workflow by allowing direct calls to service methods without writing any client code. Whether working with internal microservices or production-level APIs, grpcurl helps engineers validate gRPC service behavior efficiently.
Key Features
- No client stubs required: Works with server reflection or .proto files
- Supports JSON input and output: Makes it accessible to users familiar with REST
- TLS support: Can interact with secure endpoints
- Cross-platform: Available for Windows, macOS, and Linux
- Service discovery: Lists services and methods dynamically
Official Reference
All core details, binaries, and usage documentation are available at https://grpcurl.com.
Core Similarities Between grpcurl and cURL
Command-Line Nature
Both grpcurl and cURL are lightweight CLI-based tools. They can be executed directly in the terminal and require no additional setup apart from downloading the binary. Their command syntax is intuitive for developers comfortable with shell interfaces.
Server Communication
Each tool communicates with remote servers over a network protocol. grpcurl communicates with gRPC servers using HTTP/2 and Protocol Buffers, while cURL communicates with REST servers using HTTP/1.1 or HTTP/2 with JSON or text-based payloads.
Secure Connections
grpcurl and cURL support secure communication via TLS. Developers can configure certificates, skip verification, or use custom trust roots when connecting to secure endpoints.
Custom Headers and Payloads
Both tools allow developers to include headers and send custom payloads. For example, cURL supports -H for headers and -d for payloads, while grpcurl supports -H for headers and -d for JSON request bodies.
Human-Readable Output
Both tools’ output is easy to read and parse. Grpcurl returns JSON by default, similar to the REST responses returned by cURL.
When to Use grpcurl vs When to Use cURL
When to Use grpcurl
- Testing or debugging gRPC microservices
- Exploring APIs that use Protocol Buffers
- Working with internal systems that implement gRPC reflection
- Verifying streaming or bidirectional communication
- Securing communication with TLS for gRPC endpoints
When to Use cURL
- Testing RESTful APIs or traditional web services
- Working with public APIs using standard HTTP requests
- Performing file uploads, downloads, or HTTP-based automation
- Making authenticated requests to external web applications
- Debugging headers, response codes, and redirects
Each tool serves a unique ecosystem. grpcurl is tailored for gRPC, while cURL remains the universal standard for REST.
What These Commands Do
The first command discovers all services hosted on a gRPC server. The second one drills down into specific methods within a service. The third command invokes the GetUser method by sending a JSON-formatted payload that maps to the request structure defined in the .proto file.
Highlighting Ease of Use
With just a few flags, developers can explore, test, and validate complex RPC methods without writing a single line of client code. This is especially useful for rapid development, issue tracing, and integration testing.
Real-World Scenarios
Developer Testing Microservices
In a microservices architecture, gRPC is commonly used for internal communication within the system. Developers use grpcurl to test services before integration, ensuring correctness at each step.
Quality Assurance Teams
QA engineers validate endpoint behavior by simulating real-world requests. grpcurl allows them to create test scripts and automate API testing for gRPC services.
Debugging Service-to-Service Communication
When services fail to communicate, grpcurl helps isolate the problem. Engineers can reproduce RPC calls from the terminal to test response accuracy, latency, and error handling.
Automating Checks in CI/CD
grpcurl can be integrated into build pipelines to validate service health and compatibility before deployment. It ensures that gRPC contracts are not broken between versions.
Pros and Cons of gRPCurl vs cURL
grpcurl Pros
- No need to generate client code
- Supports server reflection
- Works directly with JSON for CLI input
- Handles complex gRPC methods and services
- Supports secure and plaintext connections
- Lightweight and easy to install
grpcurl Cons
- Slight learning curve for new users
- Requires .proto files if reflection is disabled
- Not suited for traditional REST APIs
cURL Pros
- Very easy to use and well-documented
- Works with virtually all HTTP-based APIs
- Supports a wide range of protocols and use cases
- Built into most operating systems
- Simple for quick tests, data transfers, and automation
cURL Cons
- Cannot communicate with gRPC services
- Lacks support for method-based RPC calls
- Less efficient for structured service communication
Conclusion
grpcurl and cURL both provide powerful ways to interact with APIs from the command line. While cURL is the definitive tool for REST APIs, grpcurl offers an equally capable interface for gRPC-based services.
Each tool aligns with the communication protocol it supports. grpcurl excels in gRPC environments, providing developers, testers, and DevOps teams with flexibility, efficiency, and ease of use. It supports all core features expected in modern gRPC workflows, from secure communication to reflection-based discovery.
Although they serve different ecosystems, the comparison is clear: grpcurl is the closest equivalent to cURL for gRPC APIs. Developers working in cloud-native, real-time, or microservice environments will find grpcurl to be an essential part of their toolchain.
