Persona: You are a Go API documentation engineer. You treat docs as a contract — accurate, complete annotations prevent integration bugs and make the Swagger UI the source of truth for API consumers.
Modes:
- Build — adding Swagger to a new or existing Go project: set up the toolchain, annotate handlers, generate docs, wire the UI endpoint.
- Audit — reviewing existing swagger annotations for completeness, correctness, and security coverage.
Dependencies:
- swag:
go install github.com/swaggo/swag/cmd/swag@latest
Setup
Three steps to get Swagger UI running:
swag init # generates docs/ with docs.go, swagger.json, swagger.yaml
swag init -g cmd/api/main.go # if general info is not in main.go
swag fmt # format annotation comments (like go fmt)
Import the docs package to register the spec. Use a blank import when only wiring the UI; use a named import when you also need to override docs.SwaggerInfo at runtime:
import _ "yourmodule/docs" // blank: registers spec, no identifier
import docs "yourmodule/docs" // named: use when overriding SwaggerInfo
Wire the UI endpoint — pick your framework:
// Gin
r.GET("/swagger/*any", ginSwagger.WrapHandler(swaggerFiles.Handler))
// Echo
e.GET("/swagger/*", echoSwagger.WrapHandler)
// Fiber
app.Get("/swagger/*", fiberSwagger.WrapHandler(swaggerFiles.Handler))
// net/http
mux.Handle("/swagger/", httpSwagger.Handler(swaggerFiles.Handler))
// Chi
r.Get("/swagger/*", httpSwagger.Handler(swaggerFiles.Handler))
Access the UI at /swagger/index.html.
For dynamic host/basepath (multi-environment), use a named import and override before serving:
import docs "yourmodule/docs"
docs.SwaggerInfo.Host = os.Getenv("API_HOST")
docs.SwaggerInfo.BasePath = "/api/v1"
Full CLI reference
General API Info
Place in main.go (or the file passed via -g). These annotations define the top-level spec:
// @title My API
// @version 1.0
// @description Short description of the API.
// @host localhost:8080
// @BasePath /api/v1
// @schemes http https
// @contact.name API Support
// @contact.email support@example.com
// @license.name Apache 2.0
// @securityDefinitions.apikey Bearer
// @in header
// @name Authorization
// @description Type "Bearer" followed by a space and the JWT token.
Operation Annotations
Annotate each handler function. The standard doc comment (// FuncName godoc) must precede swag annotations — it anchors indentation for swag fmt.
// ShowAccount godoc
// @Summary Get account by ID
// @Description Returns account details for the given ID.
// @Tags accounts
// @Accept json
// @Produce json
// @Param id path int true "Account ID"
// @Param filter query string false "Optional search filter"
// @Success 200 {object} model.Account
// @Success 204 "No content"
// @Failure 400 {object} api.ErrorResponse
// @Failure 404 {object} api.ErrorResponse
// @Router /accounts/{id} [get]
// @Security Bearer
func ShowAccount(c *gin.Context) {}
@Param format: @Param <name> <in> <type> <required> "<description>" [attributes]
<in> | Usage |
|---|
path | URL path segment (/users/{id}) |
query | URL query string (?filter=x) |
body | Request body — type must be a struct |
header | HTTP header |
formData | Multipart/form field |
Optional attributes on @Param: default(v), minimum(n), maximum(n), minLength(n), maxLength(n), Enums(a,b,c), example(v), collectionFormat(multi).
@Success/@Failure format: @Success <code> {<kind>} <type> "<description>"
<kind> | When |
|---|
{object} | Single struct |
{array} | Slice of structs |
string / integer | Primitive |
Generics (swag v2): @Success 200 {object} api.Response[model.User]
Nested composition: @Success 200 {object} api.Response{data=model.User}
Security Definitions
Define once at the API level (in main.go), apply per endpoint with @Security.
// Bearer / JWT
// @securityDefinitions.apikey Bearer
// @in header
// @name Authorization
// API key in header
// @securityDefinitions.apikey ApiKeyAuth
// @in header
// @name X-API-Key
// Basic auth
// @securityDefinitions.basic BasicAuth
// OAuth2 authorization code
// @securityDefinitions.oauth2.authorizationCode OAuth2
// @authorizationUrl https://example.com/oauth/authorize
// @tokenUrl https://example.com/oauth/token
// @scope.read Read access
// @scope.write Write access
Apply to an endpoint:
// @Security Bearer
// @Security OAuth2[read, write]
// @Security BasicAuth && ApiKeyAuth // AND — both required
Struct Tags
Enrich models without changing their Go type:
type CreateUserRequest struct {
Name string `json:"name" example:"Jane Doe" minLength:"2" maxLength:"100"`
Role string `json:"role" enums:"admin,user,guest" example:"user"`
Age int `json:"age" minimum:"18" maximum:"120"`
Avatar []byte `json:"avatar" swaggertype:"string" format:"base64"`
Secret string `json:"-" swaggerignore:"true"` // excluded from docs
}
| Tag | Purpose |
|---|
example | Example value shown in Swagger UI |
enums | Comma-separated allowed values |
swaggertype | Override detected type (e.g., "primitive,integer" for time.Time) |
swaggerignore:"true" | Exclude field from the generated schema |
extensions | Add OpenAPI extensions: extensions:"x-nullable,x-deprecated=true" |
Common Mistakes
| Mistake | Why it breaks | Fix |
|---|
Missing _ "yourmodule/docs" import | Schema not registered; UI loads empty | Add blank import in main.go or server init |
Stale docs/ after code changes | Docs diverge from implementation; consumers get wrong schema | Re-run swag init after every annotation change |
@Param body with primitive type | swag cannot derive schema from string; generation fails | Always use a named struct for body params |
No @Security on protected routes | Swagger UI shows no lock icon; testers send unauthenticated requests | Apply @Security to every authenticated endpoint |
| General info annotations in the wrong file | swag silently skips them; spec has no title/host | Use -g <file> flag or move annotations to main.go |
Using {object} with a map type | swag cannot generate a schema for map[string]any without help | Use a named struct or annotate with swaggertype |
Multi-word @Tags without quotes | Tags split on spaces, producing malformed grouping | Quote tags with spaces: @Tags "user accounts" |
Cross-References
- → See
samber/cc-skills-golang@golang-security for securing the Swagger UI endpoint in production (disable or gate with auth middleware).
- → See
samber/cc-skills-golang@golang-grpc for gRPC — use grpc-gateway with its own OpenAPI generator instead of swag.
This skill is not exhaustive — refer to the swaggo/swag documentation and code examples for up-to-date API signatures and usage patterns:
- For Go package docs, symbols, versions, importers, and known vulnerabilities, → See
samber/cc-skills-golang@golang-pkg-go-dev skill (godig), preferred over Context7 for Go package facts.
- To navigate this library's usage in your own code (definitions, call sites, diagnostics), → See
samber/cc-skills-golang@golang-gopls skill (gopls).
- Context7 remains a fallback for docs not indexed on pkg.go.dev.
If you encounter a bug or unexpected behavior in swag, open an issue at https://github.com/swaggo/swag/issues.