Callosum is a desktop application for designing, developing and using APIs while maintaining an OpenAPI specification. It can generate specifications from request and response examples or import a browser HAR recording. Rather than requiring a proprietary collection format or cloud synchronization, it keeps API definitions in a format teams can manage with their existing collaboration tools.
The application describes request and response schema validation, variables derived from earlier responses and Markdown documentation stored with endpoint definitions. It also includes encrypted variables for sharing secrets in a specification and supports local or restricted-network workflows. Downloads are offered for macOS, Windows and Linux. Teams can use it to keep API exploration, documentation and validation close together, while still reviewing generated schemas and deciding how specification files and credentials should be shared.
