wtf is koa-superstruct?

koa-superstruct is a small plugin that automatically checks incoming data in a Koa web application, so you don't have to write that checking logic by hand. When someone sends a request to your app, like submitting a form or posting JSON, you want to make sure the data looks right before your code tries to use it. This plugin handles that gatekeeping for you. You define a schema, which is just a description of what you expect: "the title should be a string, the id should be a number, tags should be a list of strings," and so on. You then attach that schema to a route. When a request comes in, the plugin checks the data against your description. If something doesn't match, say the title is missing when you said it's required, the plugin stops the request and sends back an HTTP 422 error with a clear message explaining what went wrong, like "Expected a value of type string for title but received undefined." At a technical level, it works as middleware, meaning it sits between the incoming request and your actual route handler. You can validate different parts of the request: the body (what was posted), the query string (URL parameters), headers, and route params. It relies on a separate validation library called superstruct, which you install alongside it. The README notes that superstruct is kept as a separate install on purpose, so you can bring your own custom types and version. This would be useful for a developer building an API with Koa who wants a lightweight way to enforce data quality without pulling in a heavy validation framework. For example, if you're building an endpoint where a client submits a blog entry with a title, body, and tags, you'd use this to make sure all required fields are present and correctly typed before your handler ever runs.