diff --git a/cmd/hooks.go b/cmd/hooks.go
index de10223..1e4c1fa 100644
--- a/cmd/hooks.go
+++ b/cmd/hooks.go
@@ -94,13 +94,53 @@ func hookSessionStart(root string) error {
 	fmt.Println("📍 Project Context:")
 	fmt.Println()
 
-	// Run codemap to show full tree structure
+	// IMPORTANT: Hook output goes directly into Claude's "Messages" context, not system prompt.
+	// This means hook output competes with conversation history for the ~200k token limit.
+	// A 1.3MB output (like a full tree of a 10k file repo) = ~500k tokens = instant context overflow.
+	//
+	// We enforce two limits:
+	// 1. Adaptive depth: larger repos get shallower trees (depth 2-4 based on file count)
+	// 2. Hard cap: 60KB max output (~15k tokens, <10% of context window)
+	//
+	// Future: Consider structured output that Claude Code can format/truncate intelligently.
 	exe, err := os.Executable()
 	if err == nil {
-		cmd := exec.Command(exe, root)
-		cmd.Stdout = os.Stdout
+		// Count files to determine appropriate depth
+		fileCount := 0
+		if state := watch.ReadState(root); state != nil {
+			fileCount = state.FileCount
+		}
+
+		// Adaptive depth: large repos get shallower trees
+		depth := "4"
+		if fileCount > 5000 {
+			depth = "2"
+		} else if fileCount > 2000 {
+			depth = "3"
+		}
+
+		cmd := exec.Command(exe, "--depth", depth, root)
+
+		// Capture output to enforce size limit
+		var buf strings.Builder
+		cmd.Stdout = &buf
 		cmd.Stderr = os.Stderr
 		cmd.Run()
+
+		output := buf.String()
+		const maxBytes = 60000 // ~15k tokens, <10% of 200k context
+
+		if len(output) > maxBytes {
+			// Truncate and add warning
+			output = output[:maxBytes]
+			// Find last newline to avoid cutting mid-line
+			if idx := strings.LastIndex(output, "\n"); idx > maxBytes-1000 {
+				output = output[:idx]
+			}
+			output += "\n\n... (truncated - repo has " + fmt.Sprintf("%d", fileCount) + " files, use `codemap .` for full tree)\n"
+		}
+
+		fmt.Print(output)
 		fmt.Println()
 	}
 
diff --git a/mcp/main.go b/mcp/main.go
index 85d836d..a00b33c 100644
--- a/mcp/main.go
+++ b/mcp/main.go
@@ -188,6 +188,19 @@ func handleGetStructure(ctx context.Context, req *mcp.CallToolRequest, input Pat
 	render.Tree(&buf, project)
 	output := stripANSI(buf.String())
 
+	// IMPORTANT: MCP tool output contributes to Claude's context window.
+	// Large repos can produce megabytes of tree output, causing instant context overflow.
+	// Cap at 60KB (~15k tokens) to stay under 10% of typical 200k context limit.
+	const maxBytes = 60000
+	if len(output) > maxBytes {
+		output = output[:maxBytes]
+		// Find last newline to avoid cutting mid-line
+		if idx := strings.LastIndex(output, "\n"); idx > maxBytes-1000 {
+			output = output[:idx]
+		}
+		output += fmt.Sprintf("\n\n... (truncated - repo has %d files, use `codemap --depth N` for full tree)\n", len(files))
+	}
+
 	// Add hub file summary
 	fg, err := scanner.BuildFileGraph(input.Path)
 	if err == nil {