diff --git a/src/SwaggerProvider.Runtime/RuntimeHelpers.fs b/src/SwaggerProvider.Runtime/RuntimeHelpers.fs
index 4807e259..504c38f3 100644
--- a/src/SwaggerProvider.Runtime/RuntimeHelpers.fs
+++ b/src/SwaggerProvider.Runtime/RuntimeHelpers.fs
@@ -343,7 +343,7 @@ module RuntimeHelpers =
                         let vTy = v.GetType()
 
                         if vTy = typeof<string> then
-                            String.Format("\"{0}\"", v)
+                            "\"" + v.ToString() + "\""
                         elif vTy.IsArray then
                             let elements =
                                 (v :?> Array)
@@ -351,13 +351,13 @@ module RuntimeHelpers =
                                 |> Seq.map(fun x -> if isNull x then "null" else x.ToString())
                                 |> Array.ofSeq
 
-                            String.Format("[{0}]", String.Join("; ", elements))
+                            "[" + String.Join("; ", elements) + "]"
                         else
                             v.ToString()
 
-                String.Format("{0}={1}", p.Name, s))
+                p.Name + "=" + s)
 
-        String.Format("{{{0}}}", String.Join("; ", strs))
+        "{" + String.Join("; ", strs) + "}"
 
     // Cached constructor for JsonPropertyNameAttribute to avoid repeated reflection lookups
     // when compiling large schemas with many properties.
@@ -501,7 +501,7 @@ module RuntimeHelpers =
             new HttpClient(handler, true, BaseAddress = Uri(host))
 
     let combineUrl (urlA: string) (urlB: string) =
-        sprintf "%s/%s" (urlA.TrimEnd('/')) (urlB.TrimStart('/'))
+        urlA.TrimEnd('/') + "/" + urlB.TrimStart('/')
 
     // Pre-built map of standard HTTP method names to their corresponding static HttpMethod
     // instances. Uses an ordinal case-insensitive comparer so callers passing different
@@ -529,18 +529,26 @@ module RuntimeHelpers =
         | true, m -> m
         | false, _ -> HttpMethod(method.ToUpperInvariant())
 
-    let createHttpRequest (httpMethod: string) address queryParams =
+    let createHttpRequest (httpMethod: string) (address: string) (queryParams: seq<string * string>) =
         let requestUrl =
-            let fakeHost = "http://fake-host/"
-            let builder = UriBuilder(combineUrl fakeHost address)
-            let query = System.Web.HttpUtility.ParseQueryString(builder.Query)
+            // Fast path: avoid UriBuilder + ParseQueryString allocation when there are no query params.
+            // TrimStart('/') mirrors the UriBuilder path's PathAndQuery.TrimStart('/') normalisation,
+            // which strips the leading slash from schema paths such as "/pets" → "pets".  A leading-
+            // slash relative URI resolves from the host root and silently drops any base path, so
+            // normalisation must be applied on both branches.
+            if Seq.isEmpty queryParams then
+                address.TrimStart('/')
+            else
+                let fakeHost = "http://fake-host/"
+                let builder = UriBuilder(combineUrl fakeHost address)
+                let query = System.Web.HttpUtility.ParseQueryString(builder.Query)
 
-            for name, value in queryParams do
-                if not <| isNull value then
-                    query.Add(name, value)
+                for name, value in queryParams do
+                    if not <| isNull value then
+                        query.Add(name, value)
 
-            builder.Query <- query.ToString()
-            builder.Uri.PathAndQuery.TrimStart('/')
+                builder.Query <- query.ToString()
+                builder.Uri.PathAndQuery.TrimStart('/')
 
         let method = resolveHttpMethod httpMethod
         new HttpRequestMessage(method, Uri(requestUrl, UriKind.Relative))
diff --git a/tests/SwaggerProvider.Tests/RuntimeHelpersTests.fs b/tests/SwaggerProvider.Tests/RuntimeHelpersTests.fs
index 5a1bbb85..e36ee868 100644
--- a/tests/SwaggerProvider.Tests/RuntimeHelpersTests.fs
+++ b/tests/SwaggerProvider.Tests/RuntimeHelpersTests.fs
@@ -553,6 +553,27 @@ module CreateHttpRequestTests =
         use req = createHttpRequest "GET" "v1/pets/42" []
         req.RequestUri.ToString() |> shouldContainText "v1/pets/42"
 
+    [<Fact>]
+    let ``createHttpRequest strips leading slash from path (no query params)``() =
+        // OpenAPI schema path keys start with '/'; the leading slash must be removed so that
+        // the relative URI is resolved relative to the HttpClient.BaseAddress path rather
+        // than from the host root.
+        use req = createHttpRequest "GET" "/pets" []
+        req.RequestUri.ToString() |> shouldEqual "pets"
+
+    [<Fact>]
+    let ``createHttpRequest strips leading slash from path (with query params)``() =
+        use req = createHttpRequest "GET" "/pets" [ ("status", "available") ]
+        let uri = req.RequestUri.ToString()
+        uri |> shouldNotContainText "/pets"
+        uri |> shouldContainText "pets"
+        uri |> shouldContainText "status=available"
+
+    [<Fact>]
+    let ``createHttpRequest strips leading slash from nested path (no query params)``() =
+        use req = createHttpRequest "GET" "/pets/42" []
+        req.RequestUri.ToString() |> shouldEqual "pets/42"
+
 
 module FillHeadersTests =