diff --git a/openapi.go b/openapi.go
index 9c181c1..93434e3 100644
--- a/openapi.go
+++ b/openapi.go
@@ -81,20 +81,25 @@ func (sb *SpecBuilder) Build(groups []RouteGroup) ([]byte, error) {
 	if sb == nil {
 		sb = &SpecBuilder{}
 	}
+	sb = sb.snapshot()
 
 	prepared := prepareRouteGroups(groups)
 
+	info := map[string]any{
+		"title":       sb.Title,
+		"description": sb.Description,
+		"version":     sb.Version,
+	}
+	if sb.Summary != "" {
+		info["summary"] = sb.Summary
+	}
+
 	spec := map[string]any{
 		"openapi":           "3.1.0",
 		"jsonSchemaDialect": openAPIDialect,
-		"info": map[string]any{
-			"title":       sb.Title,
-			"summary":     sb.Summary,
-			"description": sb.Description,
-			"version":     sb.Version,
-		},
-		"paths": sb.buildPaths(prepared),
-		"tags":  sb.buildTags(prepared),
+		"info":              info,
+		"paths":             sb.buildPaths(prepared),
+		"tags":              sb.buildTags(prepared),
 	}
 
 	if sb.LicenseName != "" {
@@ -106,12 +111,6 @@ func (sb *SpecBuilder) Build(groups []RouteGroup) ([]byte, error) {
 		}
 		spec["info"].(map[string]any)["license"] = license
 	}
-	if sb.Summary != "" {
-		spec["info"].(map[string]any)["summary"] = sb.Summary
-	} else {
-		delete(spec["info"].(map[string]any), "summary")
-	}
-
 	if swaggerPath := sb.effectiveSwaggerPath(); swaggerPath != "" {
 		spec["x-swagger-ui-path"] = normaliseSwaggerPath(swaggerPath)
 	}
@@ -1966,6 +1965,40 @@ func (sb *SpecBuilder) effectiveAuthentikPublicPaths() []string {
 	return normalisePublicPaths(paths)
 }
 
+// snapshot returns a trimmed copy of the builder so Build operates on stable
+// input even when callers reuse or mutate their original configuration.
+func (sb *SpecBuilder) snapshot() *SpecBuilder {
+	if sb == nil {
+		return &SpecBuilder{}
+	}
+
+	out := *sb
+	out.Title = strings.TrimSpace(out.Title)
+	out.Summary = strings.TrimSpace(out.Summary)
+	out.Description = strings.TrimSpace(out.Description)
+	out.Version = strings.TrimSpace(out.Version)
+	out.SwaggerPath = strings.TrimSpace(out.SwaggerPath)
+	out.GraphQLPath = strings.TrimSpace(out.GraphQLPath)
+	out.WSPath = strings.TrimSpace(out.WSPath)
+	out.SSEPath = strings.TrimSpace(out.SSEPath)
+	out.TermsOfService = strings.TrimSpace(out.TermsOfService)
+	out.ContactName = strings.TrimSpace(out.ContactName)
+	out.ContactURL = strings.TrimSpace(out.ContactURL)
+	out.ContactEmail = strings.TrimSpace(out.ContactEmail)
+	out.LicenseName = strings.TrimSpace(out.LicenseName)
+	out.LicenseURL = strings.TrimSpace(out.LicenseURL)
+	out.ExternalDocsDescription = strings.TrimSpace(out.ExternalDocsDescription)
+	out.ExternalDocsURL = strings.TrimSpace(out.ExternalDocsURL)
+	out.CacheTTL = strings.TrimSpace(out.CacheTTL)
+	out.I18nDefaultLocale = strings.TrimSpace(out.I18nDefaultLocale)
+	out.Servers = slices.Clone(sb.Servers)
+	out.I18nSupportedLocales = slices.Clone(sb.I18nSupportedLocales)
+	out.AuthentikPublicPaths = normalisePublicPaths(sb.AuthentikPublicPaths)
+	out.SecuritySchemes = cloneSecuritySchemes(sb.SecuritySchemes)
+
+	return &out
+}
+
 // isPublicOperationPath reports whether an OpenAPI path should be documented
 // as public because Authentik bypasses it in the running engine.
 func (sb *SpecBuilder) isPublicOperationPath(path string) bool {
diff --git a/openapi_test.go b/openapi_test.go
index 68c38b3..c2207ed 100644
--- a/openapi_test.go
+++ b/openapi_test.go
@@ -366,6 +366,78 @@ func TestSpecBuilder_Good_CommonResponseComponentsArePublished(t *testing.T) {
 	}
 }
 
+func TestSpecBuilder_Good_NormalisesMetadataAtBuild(t *testing.T) {
+	sb := &api.SpecBuilder{
+		Title:                   "  Test API  ",
+		Summary:                 "   ",
+		Description:             "  Trimmed description  ",
+		Version:                 "  1.2.3  ",
+		TermsOfService:          "  https://example.com/terms  ",
+		ContactName:             "  API Support  ",
+		ContactURL:              "  https://example.com/support  ",
+		ContactEmail:            "  support@example.com  ",
+		LicenseName:             "  EUPL-1.2  ",
+		LicenseURL:              "  https://eupl.eu/1.2/en/  ",
+		ExternalDocsURL:         "  https://example.com/docs  ",
+		ExternalDocsDescription: "  Developer guide  ",
+		SwaggerPath:             "  /docs/  ",
+	}
+
+	data, err := sb.Build(nil)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	var spec map[string]any
+	if err := json.Unmarshal(data, &spec); err != nil {
+		t.Fatalf("invalid JSON: %v", err)
+	}
+
+	info := spec["info"].(map[string]any)
+	if info["title"] != "Test API" {
+		t.Fatalf("expected trimmed title, got %v", info["title"])
+	}
+	if _, ok := info["summary"]; ok {
+		t.Fatal("expected blank summary to be omitted")
+	}
+	if info["description"] != "Trimmed description" {
+		t.Fatalf("expected trimmed description, got %v", info["description"])
+	}
+	if info["version"] != "1.2.3" {
+		t.Fatalf("expected trimmed version, got %v", info["version"])
+	}
+	if info["termsOfService"] != "https://example.com/terms" {
+		t.Fatalf("expected trimmed termsOfService, got %v", info["termsOfService"])
+	}
+	contact := info["contact"].(map[string]any)
+	if contact["name"] != "API Support" {
+		t.Fatalf("expected trimmed contact name, got %v", contact["name"])
+	}
+	if contact["url"] != "https://example.com/support" {
+		t.Fatalf("expected trimmed contact url, got %v", contact["url"])
+	}
+	if contact["email"] != "support@example.com" {
+		t.Fatalf("expected trimmed contact email, got %v", contact["email"])
+	}
+	license := info["license"].(map[string]any)
+	if license["name"] != "EUPL-1.2" {
+		t.Fatalf("expected trimmed licence name, got %v", license["name"])
+	}
+	if license["url"] != "https://eupl.eu/1.2/en/" {
+		t.Fatalf("expected trimmed licence url, got %v", license["url"])
+	}
+	externalDocs := spec["externalDocs"].(map[string]any)
+	if externalDocs["description"] != "Developer guide" {
+		t.Fatalf("expected trimmed external docs description, got %v", externalDocs["description"])
+	}
+	if externalDocs["url"] != "https://example.com/docs" {
+		t.Fatalf("expected trimmed external docs url, got %v", externalDocs["url"])
+	}
+	if got := spec["x-swagger-ui-path"]; got != "/docs" {
+		t.Fatalf("expected trimmed swagger path, got %v", got)
+	}
+}
+
 func TestSpecBuilder_Good_SwaggerUIPathExtension(t *testing.T) {
 	sb := &api.SpecBuilder{
 		Title:       "Test",