diff --git a/apps/web/client/src/server/api/routers/project/helper.ts b/apps/web/client/src/server/api/routers/project/helper.ts
index e2f6037378..387f78f25f 100644
--- a/apps/web/client/src/server/api/routers/project/helper.ts
+++ b/apps/web/client/src/server/api/routers/project/helper.ts
@@ -1,5 +1,12 @@
-import { type Frame } from "@onlook/db";
+import { eq } from "drizzle-orm";
+import { type Frame, projects, userProjects, type DrizzleDb } from "@onlook/db";
 
+/**
+ * Extracts the CodeSandbox preview port from an array of frames.
+ *
+ * @param frames - Array of frames to search for a CodeSandbox preview URL
+ * @returns The extracted port number if a matching CodeSandbox preview URL is found, `null` otherwise
+ */
 export function extractCsbPort(frames: Frame[]): number | null {
     if (!frames || frames.length === 0) return null;
 
@@ -17,3 +24,34 @@ export function extractCsbPort(frames: Frame[]): number | null {
     }
     return null;
 }
+
+/**
+ * Ensure the specified user has access to the specified project.
+ *
+ * @param userId - ID of the user to check
+ * @param projectId - ID of the project to check
+ * @throws Error with message 'Project not found' if no project exists with `projectId`
+ * @throws Error with message 'Unauthorized: You do not have access to this project' if the user has no access to the project
+ */
+export async function verifyProjectAccess(
+    db: DrizzleDb,
+    userId: string,
+    projectId: string,
+): Promise<void> {
+    const project = await db.query.projects.findFirst({
+        where: eq(projects.id, projectId),
+        with: {
+            userProjects: {
+                where: eq(userProjects.userId, userId),
+            },
+        },
+    });
+
+    if (!project) {
+        throw new Error('Project not found');
+    }
+
+    if (project.userProjects.length === 0) {
+        throw new Error('Unauthorized: You do not have access to this project');
+    }
+}
\ No newline at end of file
diff --git a/apps/web/client/src/server/api/routers/project/project.ts b/apps/web/client/src/server/api/routers/project/project.ts
index a110db5bbf..2747860a92 100644
--- a/apps/web/client/src/server/api/routers/project/project.ts
+++ b/apps/web/client/src/server/api/routers/project/project.ts
@@ -37,7 +37,7 @@ import { and, eq, ne } from 'drizzle-orm';
 import { z } from 'zod';
 import { projectCreateRequestRouter } from './createRequest';
 import { fork } from './fork';
-import { extractCsbPort } from './helper';
+import { extractCsbPort, verifyProjectAccess } from './helper';
 
 export const projectRouter = createTRPCRouter({
     hasAccess: protectedProcedure
@@ -348,6 +348,7 @@ export const projectRouter = createTRPCRouter({
     delete: protectedProcedure
         .input(z.object({ id: z.string() }))
         .mutation(async ({ ctx, input }) => {
+            await verifyProjectAccess(ctx.db, ctx.user.id, input.id);
             await ctx.db.transaction(async (tx) => {
                 await tx.delete(projects).where(eq(projects.id, input.id));
                 await tx.delete(userProjects).where(eq(userProjects.projectId, input.id));
@@ -365,6 +366,7 @@ export const projectRouter = createTRPCRouter({
             return projects.map((project) => fromDbProject(project.project));
         }),
     update: protectedProcedure.input(projectUpdateSchema).mutation(async ({ ctx, input }) => {
+        await verifyProjectAccess(ctx.db, ctx.user.id, input.id);
         const [updatedProject] = await ctx.db.update(projects).set({
             ...input,
             updatedAt: new Date(),
@@ -380,6 +382,7 @@ export const projectRouter = createTRPCRouter({
         projectId: z.string(),
         tag: z.string(),
     })).mutation(async ({ ctx, input }) => {
+        await verifyProjectAccess(ctx.db, ctx.user.id, input.projectId);
         const project = await ctx.db.query.projects.findFirst({
             where: eq(projects.id, input.projectId),
         });
@@ -404,6 +407,7 @@ export const projectRouter = createTRPCRouter({
         projectId: z.string(),
         tag: z.string(),
     })).mutation(async ({ ctx, input }) => {
+        await verifyProjectAccess(ctx.db, ctx.user.id, input.projectId);
         const project = await ctx.db.query.projects.findFirst({
             where: eq(projects.id, input.projectId),
         });