diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index afea5d127..b62979144 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -1,7 +1,6 @@
 # Changelog
 
 ## [Unreleased]
-
 ### Added
 
 - Added subcommands to `/copy` command: `code` (copy last code block), `all` (copy all code blocks), `cmd` (copy last bash/python command), and `last` (copy full message)
@@ -16,6 +15,7 @@
 
 ### Changed
 
+- Improved diagnostic message formatting to group errors by file path with indented details for better readability
 - Modified eager todo prelude to use hidden custom message type instead of visible developer message, preventing duplicate prompt text in session history
 - Updated eager todo prompt to remove dynamic user request injection, simplifying the template and preventing request repetition in displayed messages
 - Modified eager todo enforcement to prepend the todo reminder to the first user turn instead of executing it as a separate synthetic turn, reducing unnecessary prompt calls
diff --git a/packages/coding-agent/src/lsp/index.ts b/packages/coding-agent/src/lsp/index.ts
index 42ebcdb43..23fee0593 100644
--- a/packages/coding-agent/src/lsp/index.ts
+++ b/packages/coding-agent/src/lsp/index.ts
@@ -56,6 +56,7 @@ import {
 	formatDiagnostic,
 	formatDiagnosticsSummary,
 	formatDocumentSymbol,
+	formatGroupedDiagnosticMessages,
 	formatLocation,
 	formatSymbolInformation,
 	formatWorkspaceEdit,
@@ -1082,7 +1083,7 @@ export class LspTool implements AgentTool<typeof lspSchema, LspToolDetails, Them
 
 					const summary = formatDiagnosticsSummary(uniqueDiagnostics);
 					const formatted = uniqueDiagnostics.map(d => formatDiagnostic(d, relPath));
-					const output = `${summary}:\n${formatted.map(f => `  ${f}`).join("\n")}`;
+					const output = `${summary}:\n${formatGroupedDiagnosticMessages(formatted)}`;
 					return {
 						content: [{ type: "text", text: output }],
 						details: { action, serverName: Array.from(allServerNames).join(", "), success: true },
@@ -1094,9 +1095,8 @@ export class LspTool implements AgentTool<typeof lspSchema, LspToolDetails, Them
 				} else {
 					const summary = formatDiagnosticsSummary(uniqueDiagnostics);
 					results.push(`${theme.status.error} ${relPath}: ${summary}`);
-					for (const diag of uniqueDiagnostics) {
-						results.push(`  ${formatDiagnostic(diag, relPath)}`);
-					}
+					const formatted = uniqueDiagnostics.map(d => formatDiagnostic(d, relPath));
+					results.push(formatGroupedDiagnosticMessages(formatted));
 				}
 			}
 
diff --git a/packages/coding-agent/src/lsp/utils.ts b/packages/coding-agent/src/lsp/utils.ts
index 35b6620b1..860de6382 100644
--- a/packages/coding-agent/src/lsp/utils.ts
+++ b/packages/coding-agent/src/lsp/utils.ts
@@ -281,6 +281,87 @@ export function formatDiagnostic(diagnostic: Diagnostic, filePath: string): stri
 	return `${filePath}:${line}:${col} [${severity}] ${source}${message}${code}`;
 }
 
+// Regex: split on the first `:digits:digits` boundary to separate path from the rest
+const DIAG_PATH_RE = /^(.+?):(\d+:\d+\s+.*)$/;
+
+/**
+ * Reformat pre-formatted diagnostic messages into grep-style directory/file groups.
+ * Input:  ["path:line:col [sev] msg", ...]
+ * Output: "# dir\n## └─ file.ts\n  line:col [sev] msg"
+ *
+ * Messages that don't match the expected format are appended ungrouped at the end.
+ */
+export function formatGroupedDiagnosticMessages(messages: string[]): string {
+	const diagnosticsByFile = new Map<string, string[]>();
+	const fileOrder: string[] = [];
+	const ungrouped: string[] = [];
+
+	for (const msg of messages) {
+		const match = DIAG_PATH_RE.exec(msg);
+		if (!match) {
+			ungrouped.push(msg);
+			continue;
+		}
+
+		const [, rawFilePath, rest] = match;
+		const filePath = rawFilePath.replace(/\\/g, "/");
+		if (!diagnosticsByFile.has(filePath)) {
+			diagnosticsByFile.set(filePath, []);
+			fileOrder.push(filePath);
+		}
+		diagnosticsByFile.get(filePath)?.push(rest);
+	}
+
+	if (diagnosticsByFile.size === 0) {
+		return ungrouped.join("\n");
+	}
+
+	const filesByDirectory = new Map<string, string[]>();
+	for (const filePath of fileOrder) {
+		const directory = path.dirname(filePath).replace(/\\/g, "/");
+		if (!filesByDirectory.has(directory)) {
+			filesByDirectory.set(directory, []);
+		}
+		filesByDirectory.get(directory)?.push(filePath);
+	}
+
+	const lines: string[] = [];
+	for (const [directory, directoryFiles] of filesByDirectory) {
+		if (directory === ".") {
+			for (const filePath of directoryFiles) {
+				if (lines.length > 0) {
+					lines.push("");
+				}
+				lines.push(`# ${path.basename(filePath)}`);
+				for (const diagnostic of diagnosticsByFile.get(filePath) ?? []) {
+					lines.push(`  ${diagnostic}`);
+				}
+			}
+			continue;
+		}
+
+		if (lines.length > 0) {
+			lines.push("");
+		}
+		lines.push(`# ${directory}`);
+		for (const filePath of directoryFiles) {
+			lines.push(`## └─ ${path.basename(filePath)}`);
+			for (const diagnostic of diagnosticsByFile.get(filePath) ?? []) {
+				lines.push(`  ${diagnostic}`);
+			}
+		}
+	}
+
+	if (ungrouped.length > 0) {
+		lines.push("");
+		for (const msg of ungrouped) {
+			lines.push(msg);
+		}
+	}
+
+	return lines.join("\n");
+}
+
 /**
  * Format diagnostics grouped by severity.
  */
diff --git a/packages/coding-agent/src/tools/output-meta.ts b/packages/coding-agent/src/tools/output-meta.ts
index 37199f809..18af32bff 100644
--- a/packages/coding-agent/src/tools/output-meta.ts
+++ b/packages/coding-agent/src/tools/output-meta.ts
@@ -12,6 +12,7 @@ import type {
 	AgentToolUpdateCallback,
 } from "@oh-my-pi/pi-agent-core";
 import type { ImageContent, TextContent } from "@oh-my-pi/pi-ai";
+import { formatGroupedDiagnosticMessages } from "../lsp/utils";
 import type { Theme } from "../modes/theme/theme";
 import type { OutputSummary, TruncationResult } from "../session/streaming-output";
 import { formatBytes, wrapBrackets } from "./render-utils";
@@ -386,7 +387,7 @@ export function formatOutputNotice(meta: OutputMeta | undefined): string {
 	let diagnosticsNotice = "";
 	if (meta.diagnostics && meta.diagnostics.messages.length > 0) {
 		const d = meta.diagnostics;
-		diagnosticsNotice = `\n\nLSP Diagnostics (${d.summary}):\n  ${d.messages.join("\n  ")}`;
+		diagnosticsNotice = `\n\nLSP Diagnostics (${d.summary}):\n${formatGroupedDiagnosticMessages(d.messages)}`;
 	}
 
 	const notice = parts.length ? `\n\n[${parts.join(". ")}]` : "";