diff --git a/convex/schema.ts b/convex/schema.ts
index d6b9007..2b47c38 100644
--- a/convex/schema.ts
+++ b/convex/schema.ts
@@ -64,4 +64,10 @@ export default defineSchema({
   })
     .index("by_conversation", ["conversationId"])
     .index("by_project_status", ["projectId", "status"]),
+
+  usage: defineTable({
+    userId: v.string(),
+    messageCount: v.number(),
+    periodStart: v.number(), // Unix ms timestamp for start of current month
+  }).index("by_userId", ["userId"]),
 });
diff --git a/convex/system.ts b/convex/system.ts
index 2153ffd..22c9a84 100644
--- a/convex/system.ts
+++ b/convex/system.ts
@@ -585,6 +585,75 @@ export const createProject = mutation({
   },
 });
 
+export const checkAndIncrementUsage = mutation({
+  args: {
+    internalKey: v.string(),
+    userId: v.string(),
+    limit: v.number(),
+  },
+  handler: async (ctx, args) => {
+    validateInternalKey(args.internalKey);
+
+    const now = new Date();
+    const periodStart = Date.UTC(now.getUTCFullYear(), now.getUTCMonth(), 1);
+
+    const record = await ctx.db
+      .query("usage")
+      .withIndex("by_userId", (q) => q.eq("userId", args.userId))
+      .first();
+
+    if (!record) {
+      await ctx.db.insert("usage", {
+        userId: args.userId,
+        messageCount: 1,
+        periodStart,
+      });
+      return { allowed: true, count: 1 };
+    }
+
+    // New month — reset
+    if (record.periodStart < periodStart) {
+      await ctx.db.patch(record._id, { messageCount: 1, periodStart });
+      return { allowed: true, count: 1 };
+    }
+
+    // Over limit
+    if (record.messageCount >= args.limit) {
+      return { allowed: false, count: record.messageCount, limit: args.limit };
+    }
+
+    // Increment
+    await ctx.db.patch(record._id, { messageCount: record.messageCount + 1 });
+    return { allowed: true, count: record.messageCount + 1 };
+  },
+});
+
+export const getUserUsage = query({
+  args: {},
+  handler: async (ctx) => {
+    const identity = await ctx.auth.getUserIdentity();
+    if (!identity) return null;
+
+    const userId = identity.subject;
+    const record = await ctx.db
+      .query("usage")
+      .withIndex("by_userId", (q) => q.eq("userId", userId))
+      .first();
+
+    if (!record) return { messageCount: 0, periodStart: Date.now() };
+
+    const now = new Date();
+    const periodStart = Date.UTC(now.getUTCFullYear(), now.getUTCMonth(), 1);
+
+    // If record is from a prior month, return 0
+    if (record.periodStart < periodStart) {
+      return { messageCount: 0, periodStart };
+    }
+
+    return { messageCount: record.messageCount, periodStart: record.periodStart };
+  },
+});
+
 export const createProjectWithConversation = mutation({
   args: {
     internalKey: v.string(),
diff --git a/src/app/api/messages/route.ts b/src/app/api/messages/route.ts
index ba78c00..d0d62ac 100644
--- a/src/app/api/messages/route.ts
+++ b/src/app/api/messages/route.ts
@@ -20,9 +20,8 @@ export async function POST(request: Request) {
     return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
   }
 
-  if (!has({ plan: "pro" })) {
-    return NextResponse.json({ error: "Pro plan required" }, { status: 403 });
-  }
+  const FREE_MESSAGE_LIMIT = 10;
+  const hasPro = has({ plan: "pro" });
 
   const internalKey = process.env.HEXSMITH_CONVEX_INTERNAL_KEY;
 
@@ -36,6 +35,20 @@ export async function POST(request: Request) {
   const body = await request.json();
   const { conversationId, message } = requestSchema.parse(body);
 
+  if (!hasPro) {
+    const usage = await convex.mutation(api.system.checkAndIncrementUsage, {
+      internalKey,
+      userId,
+      limit: FREE_MESSAGE_LIMIT,
+    });
+    if (!usage.allowed) {
+      return NextResponse.json(
+        { error: "Free message limit reached", count: usage.count, limit: FREE_MESSAGE_LIMIT },
+        { status: 429 }
+      );
+    }
+  }
+
   // Call convex mutation, query
   const conversation = await convex.query(api.system.getConversationById, {
     internalKey,
diff --git a/src/features/conversations/components/conversation-sidebar.tsx b/src/features/conversations/components/conversation-sidebar.tsx
index 260a2d8..5314d3a 100644
--- a/src/features/conversations/components/conversation-sidebar.tsx
+++ b/src/features/conversations/components/conversation-sidebar.tsx
@@ -1,6 +1,8 @@
-import ky from "ky";
+import ky, { HTTPError } from "ky";
 import { toast } from "sonner";
 import { useState } from "react";
+import { useQuery } from "convex/react";
+import { useAuth, useClerk } from "@clerk/nextjs";
 import { CopyIcon, HistoryIcon, LoaderIcon, PlusIcon } from "lucide-react";
 
 import {
@@ -32,6 +34,7 @@ import {
   useCreateConversation,
   useMessages,
 } from "../hooks/use-conversations";
+import { api } from "../../../../convex/_generated/api";
 import { Id } from "../../../../convex/_generated/dataModel";
 import { DEFAULT_CONVERSATION_TITLE } from "../constants";
 import { PastConversationsDialog } from "./past-conversations-dialog";
@@ -43,6 +46,8 @@ interface ConversationSidebarProps {
 export const ConversationSidebar = ({
   projectId,
 }: ConversationSidebarProps) => {
+  const FREE_MESSAGE_LIMIT = 10;
+
   const [input, setInput] = useState("");
   const [selectedConversationId, setSelectedConversationId] =
     useState<Id<"conversations"> | null>(null);
@@ -51,6 +56,13 @@ export const ConversationSidebar = ({
     setPastConversationsOpen
   ] = useState(false);
 
+  const { has } = useAuth();
+  const { openUserProfile } = useClerk();
+  const hasPro = has ? has({ plan: "pro" }) : false;
+  const usage = useQuery(api.system.getUserUsage);
+  const messageCount = usage?.messageCount ?? 0;
+  const atLimit = !hasPro && messageCount >= FREE_MESSAGE_LIMIT;
+
   const createConversation = useCreateConversation();
   const conversations = useConversations(projectId);
 
@@ -114,8 +126,17 @@ export const ConversationSidebar = ({
           message: message.text,
         },
       });
-    } catch {
-      toast.error("Message failed to send");
+    } catch (error) {
+      if (error instanceof HTTPError && error.response.status === 429) {
+        toast.error("You've used all 10 free messages this month.", {
+          action: {
+            label: "Upgrade to Pro",
+            onClick: () => openUserProfile(),
+          },
+        });
+      } else {
+        toast.error("Message failed to send");
+      }
     }
 
     setInput("");
@@ -185,19 +206,36 @@ export const ConversationSidebar = ({
         <ConversationScrollButton />
       </Conversation>
       <div className="p-3">
+        {!hasPro && usage !== undefined && (
+          <div className="mb-2 flex items-center justify-between text-xs text-muted-foreground">
+            {atLimit ? (
+              <span className="text-destructive">
+                Message limit reached ({FREE_MESSAGE_LIMIT}/{FREE_MESSAGE_LIMIT})
+              </span>
+            ) : (
+              <span>{FREE_MESSAGE_LIMIT - messageCount} messages left this month</span>
+            )}
+            <button
+              className="underline hover:text-foreground transition-colors"
+              onClick={() => openUserProfile()}
+            >
+              Upgrade →
+            </button>
+          </div>
+        )}
         <PromptInput onSubmit={handleSubmit} className="mt-2">
           <PromptInputBody>
             <PromptInputTextarea
               placeholder="Ask Hexsmith anything..."
               onChange={(e) => setInput(e.target.value)}
               value={input}
-              disabled={isProcessing}
+              disabled={isProcessing || atLimit}
             />
           </PromptInputBody>
           <PromptInputFooter>
             <PromptInputTools />
             <PromptInputSubmit
-              disabled={isProcessing ? false : !input}
+              disabled={atLimit || (isProcessing ? false : !input)}
               status={isProcessing ? "streaming" : undefined}
             />
           </PromptInputFooter>