github.com/spf13/cobra

Cobra is the de facto standard for building CLI applications in Go, and for good reason. The API is intuitive with clear separation between commands, flags, and arguments. Error handling is predictable with typed errors that bubble up cleanly without leaking stack traces or internal state by default. The framework doesn't make crypto/TLS decisions for you since it's focused on CLI structure, which is appropriate for its scope.

From a security perspective, input validation is your responsibility—Cobra provides flag parsing but you must validate user input explicitly. This is both a strength (no hidden magic) and a risk (easy to forget). The framework doesn't include authentication/authorization primitives, which makes sense for a CLI builder but means you'll implement these from scratch. Command injection risks exist if you shell out with user input, standard Go concerns apply.

Dependency-wise, Cobra has minimal transitive dependencies and the maintainers respond to issues reasonably. The library follows secure-by-default principles where applicable: no automatic command execution, explicit flag binding, and no eval-style functionality. You control what gets executed.

Cobra is the de facto standard for building CLI tools in Go, and for good reason - it handles command routing, flag parsing, and help generation reliably. The API is intuitive once you understand the Command struct pattern, and integration with pflag gives you POSIX-compliant flag handling out of the box.

From a security perspective, Cobra is mostly unopinionated, which cuts both ways. It doesn't do automatic input validation or sanitization - you're responsible for validating all Args and flag values. The PreRunE/RunE pattern makes error handling explicit, which is good, but default error messages can leak command structure details to attackers if you're not careful about wrapping them. The library itself has a clean dependency tree (primarily pflag and yaml) which reduces supply chain risk, and the maintainers have been responsive to security issues historically.

The biggest gotcha is that shell completion generation can execute arbitrary code if you're not careful with custom completion functions. You need to be defensive about validating completion inputs, especially if your CLI interacts with external systems during tab completion.

Cobra handles the tedious work of CLI parsing while staying out of your way at runtime. Memory footprint is negligible—command structure is built once at startup and flag parsing is efficient. The generated help text is clean and the subcommand hierarchy scales well from simple tools to complex CLIs with dozens of commands. PreRun/PostRun hooks give you natural points for setup/teardown without fighting the framework.

The viper integration works but creates coupling if you're not careful—I've debugged config precedence issues where environment variables and flags interact unexpectedly. Context propagation improved in recent versions but still requires manual plumbing through command chains. Error handling is straightforward: SilenceErrors and SilenceUsage flags let you control output, though the default of printing usage on any error is annoying in production.

Configuration is code-based which I prefer for type safety, but there's no built-in support for timeouts, retries, or graceful shutdown—you wire that yourself. The lack of observability hooks means I typically wrap Execute() to add metrics and structured logging. Breaking changes between minor versions have been rare in my experience, though the 1.0 to 1.1 transition changed some flag binding behavior.