Adjust for combination of system message and funcs

Author: hmarr

src/index.ts

@@ -20,6 +20,12 @@ export function promptTokensEstimate({ messages, functions }: { messages: Messag
   if (functions) {
     tokens += functionsTokensEstimate(functions as any as FunctionDef[]);
   }
+
+  // If there's a system message _and_ functions are present, subtract three tokens
+  if (functions && messages.find(m => m.role === "system")) {
+    tokens -= 3;
+  }
+
   return tokens;
 }
 

tests/token-counts.test.ts

@@ -148,6 +148,19 @@ const TEST_CASES: Example[] = [
       { role: "assistant", content: "", function_call: { name: "do_stuff", arguments: `{"foo":"bar", "baz":\n\n 1.5}` } },
     ],
     tokens: 25,
+  },
+  {
+    messages: [
+      { "role": "system", "content": "Hello" },
+      { "role": "user", "content": "Hi there" },
+    ],
+    functions: [
+      {
+        "name": "do_stuff",
+        "parameters": { "type": "object", "properties": {} }
+      }
+    ],
+    tokens: 35,
   }
 ];