diff --git a/packages/llm/src/prompts/architecture-overview.ts b/packages/llm/src/prompts/architecture-overview.ts
new file mode 100644
index 0000000..9161ab4
--- /dev/null
+++ b/packages/llm/src/prompts/architecture-overview.ts
@@ -0,0 +1,51 @@
+import type { LLMMessage, CodeStructure } from "@codeboard/shared";
+
+export function buildArchitecturePrompt(
+  structure: CodeStructure
+): LLMMessage[] {
+  const fileTree = structure.files
+    .map((f) => `  ${f.path} (${f.language}, ${f.functions.length} functions, ${f.classes.length} classes)`)
+    .join("\n");
+
+  const modules = structure.modules
+    .map((m) => `  ${m.name}/ (${m.files.length} files)`)
+    .join("\n");
+
+  const entryPoints = structure.entryPoints.join(", ") || "none detected";
+
+  return [
+    {
+      role: "system",
+      content: `You are an expert software architect analyzing a codebase. Generate a concise architecture overview and a Mermaid flowchart diagram.
+
+Output format (use exactly these headers):
+## Architecture Overview
+[2-4 paragraphs describing high-level architecture, key design decisions, and how components interact]
+
+## Tech Stack
+[comma-separated list of technologies detected]
+
+## Mermaid Diagram
+\`\`\`mermaid
+[flowchart TD diagram showing modules and their relationships]
+\`\`\``,
+    },
+    {
+      role: "user",
+      content: `Analyze this codebase structure:
+
+FILE TREE:
+${fileTree}
+
+MODULES:
+${modules}
+
+ENTRY POINTS: ${entryPoints}
+
+DEPENDENCIES (import edges):
+${structure.dependencies.slice(0, 50).map((d) => `  ${d.source} -> ${d.target}`).join("\n")}
+
+Generate architecture overview with a Mermaid diagram.`,
+    },
+  ];
+}