All 15 Endpoint Metadata, Route Constraints & Templates questions
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How do route constraints (like {id:int} or {id:guid}) restrict which requests match a given route, and why are they useful? What is endpoint metadata, and how do attributes like [Authorize] and custom metadata attach to a specific route for later inspection by middleware? How does route template precedence work when multiple routes could potentially match the same incoming URL? How do you define optional route parameters, and what's the difference between an optional parameter and one with a default value? How do route parameter transformers let you customize the casing convention of generated URLs, such as converting PascalCase action names to kebab-case URLs? How do complex/composite route segments (combining literal text and a parameter in the same segment, like {fileName}.{extension}) work? How would you implement a custom route constraint (IRouteConstraint) for a domain-specific validation pattern, like a product SKU format? How do you write custom middleware or an endpoint filter that reads endpoint metadata to conditionally alter its behavior per-route? How would you implement a catch-all route parameter to handle a variable-depth URL path, like a file browser or wiki-style page hierarchy? How would you implement route-based API versioning using route templates and constraints without a dedicated versioning library?
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ASP.NET Core › Endpoint Metadata, Route Constraints & Templates

What is route grouping via MapGroup, and how does it let you apply shared route prefixes, metadata, and filters to a set of related minimal API endpoints?

Intermediate

Answer

MapGroup("/prefix") returns a RouteGroupBuilder that automatically prepends the given prefix to every endpoint mapped within it, and any metadata, authorization requirements, or filters applied to the group (via .RequireAuthorization(), .AddEndpointFilter(), .WithTags()) automatically apply to all endpoints in that group, reducing repetition for a cohesive set of related routes.
var productsGroup = app.MapGroup("/api/products")
    .RequireAuthorization()
    .WithTags("Products");

productsGroup.MapGet("/", GetAll);           // -> /api/products, requires auth
productsGroup.MapGet("/{id}", GetById);      // -> /api/products/{id}, requires auth
productsGroup.MapPost("/", Create);          // -> /api/products, requires auth
Real-world example A minimal API organizes all product-related endpoints under one MapGroup call, applying shared authorization and Swagger tagging once at the group level instead of repeating the same configuration on every individual endpoint registration.

Common follow-ups: Can route groups be nested for even finer-grained shared configuration?;How does grouping interact with API versioning's own grouping mechanisms?

Controllers vs Minimal APIs;API Documentation with Swagger/OpenAPI
All 15 Endpoint Metadata, Route Constraints & Templates questions