diff --git a/packages/api/session.mts b/packages/api/session.mts
index 21560ca0..b4220491 100644
--- a/packages/api/session.mts
+++ b/packages/api/session.mts
@@ -30,6 +30,7 @@ import { fileExists } from './fs-utils.mjs';
 import { validFilename } from '@srcbook/shared';
 import { pathToCodeFile } from './srcbook/path.mjs';
 import { exec } from 'node:child_process';
+import { npmInstall } from './exec.mjs';
 
 const sessions: Record<string, SessionType> = {};
 
@@ -297,10 +298,42 @@ export function updateCell(session: SessionType, cell: CellType, updates: CellUp
       return updateCodeCell(session, cell, updates);
   }
 }
-
-export async function formatCode(filePath: string) {
+async function ensurePrettierInstalled(dir: string): Promise<boolean> {
+  const prettierPath = Path.join(dir, 'node_modules', 'prettier');
   try {
-    const command = `npx prettier ${filePath}`;
+    // check if prettier is installed
+    await fs.access(prettierPath);
+    return true;
+  } catch (error) {
+    return new Promise<boolean>((resolve) => {
+      try {
+        npmInstall({
+          cwd: dir,
+          packages: ['prettier'],
+          stdout: () => {},
+          stderr: (err) => console.error(err),
+          onExit: (exitCode) => {
+            if (exitCode === 0) {
+              resolve(true);
+            } else {
+              console.error('Failed to install Prettier:', exitCode);
+              resolve(false);
+            }
+          },
+        });
+      } catch (installError) {
+        console.error('Failed to initiate Prettier installation:', installError);
+        resolve(false);
+      }
+    });
+  }
+}
+export async function formatCode(dir: string, fileName: string) {
+  try {
+    await ensurePrettierInstalled(dir);
+
+    const codeFilePath = pathToCodeFile(dir, fileName);
+    const command = `npx prettier ${codeFilePath}`;
 
     return new Promise((resolve, reject) => {
       exec(command, async (error, stdout) => {
@@ -319,7 +352,7 @@ export async function formatCode(filePath: string) {
 }
 export async function formatAndUpdateCodeCell(session: SessionType, cell: CodeCellType) {
   try {
-    const formattedCode = await formatCode(pathToCodeFile(session.dir, cell.filename));
+    const formattedCode = await formatCode(session.dir, cell.filename);
     return updateCodeCell(session, cell, { source: formattedCode } as { source: string });
   } catch (error) {
     return Promise.resolve({
diff --git a/packages/api/srcbook/config.mts b/packages/api/srcbook/config.mts
index d1141158..5ad9d778 100644
--- a/packages/api/srcbook/config.mts
+++ b/packages/api/srcbook/config.mts
@@ -1,14 +1,12 @@
 export function buildJSPackageJson() {
   return {
     type: 'module',
-    dependencies: {
+    devDependencies: {
       prettier: 'latest',
     },
     prettier: {
-      tabWidth: 2,
       semi: true,
       singleQuote: true,
-      printWidth: 100,
     },
   };
 }
@@ -20,13 +18,13 @@ export function buildTSPackageJson() {
       tsx: 'latest',
       typescript: 'latest',
       '@types/node': 'latest',
+    },
+    devDependencies: {
       prettier: 'latest',
     },
     prettier: {
-      tabWidth: 2,
       semi: true,
       singleQuote: true,
-      printWidth: 100,
     },
   };
 }