diff --git a/index.js b/index.js
index dcce15c..19af543 100644
--- a/index.js
+++ b/index.js
@@ -53,11 +53,20 @@ export default async function jsonSchemaToDiagram(options) {
     throw new Error("Missing required options");
   }
 
-  const fileToUpdatePath = path.join(__dirname, filePath);
+  const fileToUpdatePath = path.isAbsolute(filePath)
+    ? filePath
+    : path.resolve(process.cwd(), filePath);
 
   try {
     const data = await readFile(fileToUpdatePath, "utf8");
 
+    const regex = new RegExp(`${startMarker}[\\s\\S]*?${endMarker}`, "g");
+
+    if (!regex.test(data)) {
+      console.error(`Markers not found in ${fileToUpdatePath}`);
+      return;
+    }
+
     const {
       object: { mermaidDiagramString },
     } = await generateObject({
@@ -75,21 +84,14 @@ export default async function jsonSchemaToDiagram(options) {
 
     const diagramContent = `\`\`\`mermaid\n${mermaidDiagramString}\n\`\`\`\n`;
 
-    const regex = new RegExp(`${startMarker}[\\s\\S]*?${endMarker}`, "g");
-
-    if (!regex.test(data)) {
-      console.error(`Markers not found in ${filePath}.`);
-      return;
-    }
-
     const newContent = data.replace(
       regex,
       `${startMarker}\n${diagramContent}${endMarker}`
     );
 
     await writeFile(fileToUpdatePath, newContent, "utf8");
-    console.log(`Diagram successfully updated in ${filePath}`);
+    console.log(`Diagram successfully updated in ${fileToUpdatePath}`);
   } catch (err) {
-    console.error(`Error processing ${filePath}:`, err);
+    console.error(`Error processing ${fileToUpdatePath}:`, err);
   }
 }
diff --git a/index.test.js b/index.test.js
index 6c260b7..04bb297 100644
--- a/index.test.js
+++ b/index.test.js
@@ -1,6 +1,8 @@
 import { describe, beforeEach, it, expect, vi, afterEach } from "vitest";
 import path from "path";
-import { fs, vol } from "memfs";
+import { fs, Volume } from "memfs";
+
+const vol = new Volume();
 
 vi.mock("node:fs");
 vi.mock("node:fs/promises");
@@ -9,14 +11,19 @@ describe("jsonSchemaToDiagram", () => {
   let jsonSchemaToDiagram;
   const startMarker = "<!-- MERMAID_DIAGRAM_START -->";
   const endMarker = "<!-- MERMAID_DIAGRAM_END -->";
+  const resolvedPath = path.resolve(process.cwd(), "./README.md");
+  const filePath = "./README.md";
 
   beforeEach(async () => {
-    vi.restoreAllMocks();
     process.env.OPENAI_API_KEY = "test-api-key";
-    vol.reset();
+
+    vi.mock("node:fs/promises", async () => {
+      const memfs = await vi.importActual("memfs");
+      return memfs.fs.promises;
+    });
 
     vol.fromJSON({
-      "./README.md":
+      resolvedPath:
         "<!-- MERMAID_DIAGRAM_START -->\nOld content\n<!-- MERMAID_DIAGRAM_END -->",
     });
 
@@ -32,6 +39,7 @@ describe("jsonSchemaToDiagram", () => {
   });
 
   afterEach(() => {
+    vol.reset();
     vi.restoreAllMocks();
   });
 
@@ -55,7 +63,6 @@ describe("jsonSchemaToDiagram", () => {
   });
 
   it.todo("updates file with generated mermaid diagram", async () => {
-    const filePath = "./README.md";
     const systemPrompt = "test system prompt";
     const model = "test model";
     const jsonSchema = { tools: [] };
@@ -83,13 +90,12 @@ describe("jsonSchemaToDiagram", () => {
   });
 
   it.todo("logs error if markers are not found in file", async () => {
-    const filePath = "./README.md";
     const systemPrompt = "test system prompt";
     const model = "test model";
     const jsonSchema = { tools: [] };
 
     vol.fromJSON({
-      "./README.md": "No markers here",
+      resolvedPath: "No markers here",
     });
 
     vi.spyOn(console, "error").mockImplementation(() => {});
@@ -109,14 +115,18 @@ describe("jsonSchemaToDiagram", () => {
     );
   });
 
-  it("logs error if there is an error processing the file", async () => {
-    const filePath = "./README.md";
+  it("logs error if the LLM fails to generate the diagram", async () => {
     const systemPrompt = "test system prompt";
     const model = "test model";
     const jsonSchema = { tools: [] };
 
     vi.spyOn(console, "error").mockImplementation(() => {});
 
+    vi.mock("ai", () => ({
+      __esModule: true,
+      generateObject: vi.fn().mockRejectedValue(new Error("Processing failed")),
+    }));
+
     await jsonSchemaToDiagram({
       filePath,
       startMarker,
@@ -127,7 +137,7 @@ describe("jsonSchemaToDiagram", () => {
     });
 
     expect(console.error).toHaveBeenCalledWith(
-      `Error processing ${filePath}:`,
+      `Error processing ${resolvedPath}:`,
       expect.any(Error)
     );
   });
diff --git a/readme.md b/readme.md
index b00d993..9786d20 100644
--- a/readme.md
+++ b/readme.md
@@ -47,6 +47,17 @@ npm install --save-dev json-schema-to-diagram
 
 ## Usage
 
+1. Add a start and end marker to your README.md file.
+
+```md
+## Function Calling Tools - Diagram
+
+<!-- MERMAID_DIAGRAM_START -->
+<!-- MERMAID_DIAGRAM_END -->
+```
+
+2. Get the JSON schema of your function calling tools and generate the diagram by calling `jsonSchemaToDiagram` with the `jsonSchema` option.
+
 ```js
 import jsonSchemaToDiagram from "json-schema-to-diagram";
 
@@ -62,7 +73,6 @@ const TOOLS = {
       filePath: "./README.md",
       jsonSchema: TOOLS,
     });
-    console.log("Diagram appended successfully.");
   } catch (error) {
     console.error("Error appending diagram:", error);
     process.exit(1);