diff --git a/package-lock.json b/package-lock.json
index df56d3a..8e6519f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -15,6 +15,7 @@
         "@types/jest": "^29.5.3",
         "jest": "^29.6.1",
         "openai": "^4.2.0",
+        "prettier": "^3.0.2",
         "ts-jest": "^29.1.1",
         "typescript": "^5.1.6"
       }
@@ -3253,6 +3254,21 @@
         "node": ">=8"
       }
     },
+    "node_modules/prettier": {
+      "version": "3.0.2",
+      "resolved": "https://registry.npmjs.org/prettier/-/prettier-3.0.2.tgz",
+      "integrity": "sha512-o2YR9qtniXvwEZlOKbveKfDQVyqxbEIWn48Z8m3ZJjBjcCmUy3xZGIv+7AkaeuaTr6yPXJjwv07ZWlsWbEy1rQ==",
+      "dev": true,
+      "bin": {
+        "prettier": "bin/prettier.cjs"
+      },
+      "engines": {
+        "node": ">=14"
+      },
+      "funding": {
+        "url": "https://github.com/prettier/prettier?sponsor=1"
+      }
+    },
     "node_modules/pretty-format": {
       "version": "29.6.1",
       "resolved": "https://registry.npmjs.org/pretty-format/-/pretty-format-29.6.1.tgz",
diff --git a/package.json b/package.json
index 3d79bdf..a691555 100644
--- a/package.json
+++ b/package.json
@@ -10,7 +10,8 @@
   "scripts": {
     "test": "jest",
     "build": "tsc",
-    "prepublishOnly": "npm run build"
+    "prepublishOnly": "npm run build",
+    "lint": "prettier --check src tests"
   },
   "author": {
     "email": "harry@hmarr.com",
@@ -26,10 +27,14 @@
     "@types/jest": "^29.5.3",
     "jest": "^29.6.1",
     "openai": "^4.2.0",
+    "prettier": "^3.0.2",
     "ts-jest": "^29.1.1",
     "typescript": "^5.1.6"
   },
   "dependencies": {
     "js-tiktoken": "^1.0.7"
+  },
+  "prettier": {
+    "trailingComma": "all"
   }
-}
+}
\ No newline at end of file
diff --git a/src/functions.ts b/src/functions.ts
index 94498c0..a5a5eb5 100644
--- a/src/functions.ts
+++ b/src/functions.ts
@@ -22,24 +22,24 @@ interface ObjectProp {
 type Prop = {
   description?: string;
 } & (
-    | ObjectProp
-    | {
+  | ObjectProp
+  | {
       type: "string";
       enum?: string[];
     }
-    | {
+  | {
       type: "number" | "integer";
       minimum?: number;
       maximum?: number;
       enum?: number[];
     }
-    | { type: "boolean" }
-    | { type: "null" }
-    | {
+  | { type: "boolean" }
+  | { type: "null" }
+  | {
       type: "array";
       items?: Prop;
     }
-  );
+);
 
 // When OpenAI use functions in the prompt, they format them as TypeScript definitions rather than OpenAPI JSON schemas.
 // This function converts the JSON schemas into TypeScript definitions.
@@ -75,7 +75,7 @@ function formatObjectProperties(obj: ObjectProp, indent: number): string {
       lines.push(`${name}?: ${formatType(param, indent)},`);
     }
   }
-  return lines.map(line => ' '.repeat(indent) + line).join("\n");
+  return lines.map((line) => " ".repeat(indent) + line).join("\n");
 }
 
 // Format a single property type
@@ -108,4 +108,4 @@ function formatType(param: Prop, indent: number): string {
       }
       return "any[]";
   }
-}
\ No newline at end of file
+}
diff --git a/src/index.ts b/src/index.ts
index 50a41ab..58dd2d0 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -14,17 +14,25 @@ let encoder: Tiktoken | undefined;
  * @param {Function[]} prompt.functions OpenAI function definitions
  * @returns An estimate for the number of tokens the prompt will use
  */
-export function promptTokensEstimate({ messages, functions }: { messages: Message[], functions?: Function[] }): number {
+export function promptTokensEstimate({
+  messages,
+  functions,
+}: {
+  messages: Message[];
+  functions?: Function[];
+}): number {
   // It appears that if functions are present, the first system message is padded with a trailing newline. This
   // was inferred by trying lots of combinations of messages and functions and seeing what the token counts were.
   let paddedSystem = false;
-  let tokens = messages.map(m => {
-    if (m.role === "system" && functions && !paddedSystem) {
-      m = { ...m, content: m.content + "\n" }
-      paddedSystem = true;
-    }
-    return messageTokensEstimate(m);
-  }).reduce((a, b) => a + b, 0);
+  let tokens = messages
+    .map((m) => {
+      if (m.role === "system" && functions && !paddedSystem) {
+        m = { ...m, content: m.content + "\n" };
+        paddedSystem = true;
+      }
+      return messageTokensEstimate(m);
+    })
+    .reduce((a, b) => a + b, 0);
 
   // Each completion (vs message) seems to carry a 3-token overhead
   tokens += 3;
@@ -37,7 +45,7 @@ export function promptTokensEstimate({ messages, functions }: { messages: Messag
   // If there's a system message _and_ functions are present, subtract four tokens. I assume this is because
   // functions typically add a system message, but reuse the first one if it's already there. This offsets
   // the extra 9 tokens added by the function definitions.
-  if (functions && messages.find(m => m.role === "system")) {
+  if (functions && messages.find((m) => m.role === "system")) {
     tokens -= 4;
   }
 
@@ -68,7 +76,7 @@ export function messageTokensEstimate(message: Message): number {
     message.content,
     message.name,
     message.function_call?.name,
-    message.function_call?.arguments
+    message.function_call?.arguments,
   ].filter((v): v is string => !!v);
   let tokens = components.map(stringTokens).reduce((a, b) => a + b, 0);
   tokens += 3; // Add three per message
@@ -85,7 +93,7 @@ export function messageTokensEstimate(message: Message): number {
 }
 
 /**
- * Estimate the number of tokens a function definition will use. Note that using the function definition within 
+ * Estimate the number of tokens a function definition will use. Note that using the function definition within
  * a prompt will add extra tokens, so you might want to use `promptTokensEstimate` instead.
  * @param funcs An array of OpenAI function definitions
  * @returns An estimate for the number of tokens the function definitions will use
diff --git a/tests/token-counts.test.ts b/tests/token-counts.test.ts
index a152dd0..2d9ec03 100644
--- a/tests/token-counts.test.ts
+++ b/tests/token-counts.test.ts
@@ -7,7 +7,7 @@ type Example = {
   messages: Message[];
   functions?: Function[];
   tokens: number;
-  validate?: boolean
+  validate?: boolean;
 };
 
 const TEST_CASES: Example[] = [
@@ -76,27 +76,19 @@ const TEST_CASES: Example[] = [
   },
   // these are all random test cases below
   {
-    messages: [
-      { role: "user", content: "hello" }
-    ],
-    tokens: 8
+    messages: [{ role: "user", content: "hello" }],
+    tokens: 8,
   },
   {
-    messages: [
-      { role: "user", content: "hello world" }
-    ],
-    tokens: 9
+    messages: [{ role: "user", content: "hello world" }],
+    tokens: 9,
   },
   {
-    messages: [
-      { role: "system", content: "hello" }
-    ],
+    messages: [{ role: "system", content: "hello" }],
     tokens: 8,
   },
   {
-    messages: [
-      { role: "system", content: "hello:" }
-    ],
+    messages: [{ role: "system", content: "hello:" }],
     tokens: 9,
   },
   {
@@ -105,37 +97,31 @@ const TEST_CASES: Example[] = [
       { role: "user", content: "hello robot" },
       { role: "assistant", content: "hello world" },
     ],
-    tokens: 27
+    tokens: 27,
   },
   {
-    messages: [
-      { role: "user", content: "hello" }
-    ],
+    messages: [{ role: "user", content: "hello" }],
     functions: [
       {
         name: "foo",
-        parameters: { type: "object", properties: {} }
-      }
+        parameters: { type: "object", properties: {} },
+      },
     ],
-    tokens: 31
+    tokens: 31,
   },
   {
-    messages: [
-      { role: "user", content: "hello" }
-    ],
+    messages: [{ role: "user", content: "hello" }],
     functions: [
       {
         name: "foo",
         description: "Do a foo",
-        parameters: { type: "object", properties: {} }
-      }
+        parameters: { type: "object", properties: {} },
+      },
     ],
-    tokens: 36
+    tokens: 36,
   },
   {
-    messages: [
-      { role: "user", content: "hello" }
-    ],
+    messages: [{ role: "user", content: "hello" }],
     functions: [
       {
         name: "bing_bong",
@@ -144,16 +130,14 @@ const TEST_CASES: Example[] = [
           type: "object",
           properties: {
             foo: { type: "string" },
-          }
-        }
-      }
+          },
+        },
+      },
     ],
-    tokens: 49
+    tokens: 49,
   },
   {
-    messages: [
-      { role: "user", content: "hello" }
-    ],
+    messages: [{ role: "user", content: "hello" }],
     functions: [
       {
         name: "bing_bong",
@@ -163,16 +147,14 @@ const TEST_CASES: Example[] = [
           properties: {
             foo: { type: "string" },
             bar: { type: "number", description: "A number" },
-          }
-        }
-      }
+          },
+        },
+      },
     ],
     tokens: 57,
   },
   {
-    messages: [
-      { role: "user", content: "hello" }
-    ],
+    messages: [{ role: "user", content: "hello" }],
     functions: [
       {
         name: "bing_bong",
@@ -184,12 +166,12 @@ const TEST_CASES: Example[] = [
               type: "object",
               properties: {
                 bar: { type: "string", enum: ["a", "b", "c"] },
-                baz: { type: "boolean" }
-              }
+                baz: { type: "boolean" },
+              },
             },
-          }
-        }
-      }
+          },
+        },
+      },
     ],
     tokens: 68,
   },
@@ -203,100 +185,122 @@ const TEST_CASES: Example[] = [
   {
     messages: [
       { role: "user", content: "hello world" },
-      { role: "function", name: "do_stuff", content: `{"foo": "bar", "baz": 1.5}` },
+      {
+        role: "function",
+        name: "do_stuff",
+        content: `{"foo": "bar", "baz": 1.5}`,
+      },
     ],
     tokens: 28,
   },
   {
     messages: [
-      { role: "function", name: "dance_the_tango", content: `{"a": { "b" : { "c": false}}}` },
+      {
+        role: "function",
+        name: "dance_the_tango",
+        content: `{"a": { "b" : { "c": false}}}`,
+      },
     ],
     tokens: 24,
   },
   {
     messages: [
-      { role: "assistant", content: "", function_call: { name: "do_stuff", arguments: `{"foo": "bar", "baz": 1.5}` } },
+      {
+        role: "assistant",
+        content: "",
+        function_call: {
+          name: "do_stuff",
+          arguments: `{"foo": "bar", "baz": 1.5}`,
+        },
+      },
     ],
     tokens: 26,
   },
   {
     messages: [
-      { role: "assistant", content: "", function_call: { name: "do_stuff", arguments: `{"foo":"bar", "baz":\n\n 1.5}` } },
+      {
+        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" },
+      { role: "system", content: "Hello" },
+      { role: "user", content: "Hi there" },
     ],
     functions: [
       {
-        "name": "do_stuff",
-        "parameters": { "type": "object", "properties": {} }
-      }
+        name: "do_stuff",
+        parameters: { type: "object", properties: {} },
+      },
     ],
     tokens: 35,
   },
   {
     messages: [
-      { "role": "system", "content": "Hello:" },
-      { "role": "user", "content": "Hi there" },
+      { role: "system", content: "Hello:" },
+      { role: "user", content: "Hi there" },
     ],
     functions: [
-      { "name": "do_stuff", "parameters": { "type": "object", "properties": {} } }
+      { name: "do_stuff", parameters: { type: "object", properties: {} } },
     ],
     tokens: 35,
   },
   {
     messages: [
-      { "role": "system", "content": "Hello:" },
-      { "role": "system", "content": "Hello" },
-      { "role": "user", "content": "Hi there" },
+      { role: "system", content: "Hello:" },
+      { role: "system", content: "Hello" },
+      { role: "user", content: "Hi there" },
     ],
     functions: [
-      { "name": "do_stuff", "parameters": { "type": "object", "properties": {} } }
+      { name: "do_stuff", parameters: { type: "object", properties: {} } },
     ],
     tokens: 40,
   },
   {
-    messages: [{ role: 'user', content: 'hello' }],
+    messages: [{ role: "user", content: "hello" }],
     functions: [
       {
-        name: 'get_recipe',
+        name: "get_recipe",
         parameters: {
-          type: 'object',
-          required: ['ingredients', 'instructions', 'time_to_cook'],
+          type: "object",
+          required: ["ingredients", "instructions", "time_to_cook"],
           properties: {
             ingredients: {
-              type: 'array',
+              type: "array",
               items: {
-                type: 'object',
-                required: ['name', 'unit', 'amount'],
+                type: "object",
+                required: ["name", "unit", "amount"],
                 properties: {
                   name: {
-                    type: 'string',
+                    type: "string",
                   },
                   unit: {
-                    enum: ['grams', 'ml', 'cups', 'pieces', 'teaspoons'],
-                    type: 'string',
+                    enum: ["grams", "ml", "cups", "pieces", "teaspoons"],
+                    type: "string",
                   },
                   amount: {
-                    type: 'number',
+                    type: "number",
                   },
                 },
               },
             },
             instructions: {
-              type: 'array',
+              type: "array",
               items: {
-                type: 'string',
+                type: "string",
               },
-              description: 'Steps to prepare the recipe (no numbering)',
+              description: "Steps to prepare the recipe (no numbering)",
             },
             time_to_cook: {
-              type: 'number',
-              description: 'Total time to prepare the recipe in minutes',
+              type: "number",
+              description: "Total time to prepare the recipe in minutes",
             },
           },
         },
@@ -305,101 +309,104 @@ const TEST_CASES: Example[] = [
     tokens: 106,
   },
   {
-    messages: [{ role: 'user', content: 'hello' }],
+    messages: [{ role: "user", content: "hello" }],
     functions: [
       {
-        name: 'function',
-        description: 'description',
+        name: "function",
+        description: "description",
         parameters: {
-          type: 'object',
+          type: "object",
           properties: {
             quality: {
-              type: 'object',
+              type: "object",
               properties: {
                 pros: {
-                  type: 'array',
+                  type: "array",
                   items: {
-                    type: 'string',
+                    type: "string",
                   },
-                  description: 'Write 3 points why this text is well written',
-                }
+                  description: "Write 3 points why this text is well written",
+                },
               },
-            }
+            },
           },
-        }
-      }],
+        },
+      },
+    ],
     tokens: 46,
   },
   {
-    messages: [{ role: 'user', content: 'hello' }],
+    messages: [{ role: "user", content: "hello" }],
     functions: [
       {
-        name: 'function',
-        description: 'desctiption1',
+        name: "function",
+        description: "desctiption1",
         parameters: {
-          type: 'object',
-          description: 'desctiption2',
+          type: "object",
+          description: "desctiption2",
           properties: {
             mainField: {
-              type: 'string',
-              description: 'description3',
+              type: "string",
+              description: "description3",
             },
-            'field number one': {
-              type: 'object',
-              description: 'description4',
+            "field number one": {
+              type: "object",
+              description: "description4",
               properties: {
                 yesNoField: {
-                  type: 'string',
-                  description: 'description5',
-                  enum: [
-                    'Yes',
-                    'No',
-                  ],
+                  type: "string",
+                  description: "description5",
+                  enum: ["Yes", "No"],
                 },
                 howIsInteresting: {
-                  type: 'string',
-                  description: 'description6',
+                  type: "string",
+                  description: "description6",
                 },
                 scoreInteresting: {
-                  type: 'number',
-                  description: 'description7',
+                  type: "number",
+                  description: "description7",
                 },
                 isInteresting: {
-                  type: 'string',
-                  description: 'description8',
-                  enum: [
-                    'Yes',
-                    'No',
-                  ],
+                  type: "string",
+                  description: "description8",
+                  enum: ["Yes", "No"],
                 },
               },
             },
           },
-
-        }
-      }
+        },
+      },
     ],
     tokens: 96,
-  }
+  },
 ];
 
 const validateAll = false;
 const openAITimeout = 10000;
 
 describe.each(TEST_CASES)("token counts (%j)", (example) => {
-  const validateTest = ((validateAll || example.validate) ? test : test.skip)
-  validateTest("test data matches openai", async () => {
-    const openai = new OpenAI();
-    const response = await openai.chat.completions.create({
-      model: "gpt-3.5-turbo",
-      messages: example.messages,
-      functions: example.functions as any,
-      max_tokens: 10,
-    });
-    expect(response.usage?.prompt_tokens).toBe(example.tokens);
-  }, openAITimeout);
+  const validateTest = validateAll || example.validate ? test : test.skip;
+  validateTest(
+    "test data matches openai",
+    async () => {
+      const openai = new OpenAI();
+      const response = await openai.chat.completions.create({
+        model: "gpt-3.5-turbo",
+        messages: example.messages,
+        functions: example.functions as any,
+        max_tokens: 10,
+      });
+      expect(response.usage?.prompt_tokens).toBe(example.tokens);
+    },
+    openAITimeout,
+  );
 
   test("estimate is correct", async () => {
-    expect(promptTokensEstimate({ messages: example.messages, functions: example.functions })).toBe(example.tokens);
+    expect(
+      promptTokensEstimate({
+        messages: example.messages,
+        functions: example.functions,
+      }),
+    ).toBe(example.tokens);
   });
-})
\ No newline at end of file
+});