diff --git a/src/tools/grep/cli.ts b/src/tools/grep/cli.ts
index 6109139b5..c44bda377 100644
--- a/src/tools/grep/cli.ts
+++ b/src/tools/grep/cli.ts
@@ -95,7 +95,7 @@ function buildArgs(options: GrepOptions, backend: GrepBackend): string[] {
   return backend === "rg" ? buildRgArgs(options) : buildGrepArgs(options)
 }
 
-function parseOutput(output: string): GrepMatch[] {
+function parseOutput(output: string, filesOnly = false): GrepMatch[] {
   if (!output.trim()) return []
 
   const matches: GrepMatch[] = []
@@ -104,6 +104,16 @@ function parseOutput(output: string): GrepMatch[] {
   for (const line of lines) {
     if (!line.trim()) continue
 
+    if (filesOnly) {
+      // --files-with-matches outputs only file paths, one per line
+      matches.push({
+        file: line.trim(),
+        line: 0,
+        text: "",
+      })
+      continue
+    }
+
     const match = line.match(/^(.+?):(\d+):(.*)$/)
     if (match) {
       matches.push({
@@ -191,7 +201,7 @@ async function runRgInternal(options: GrepOptions): Promise<GrepResult> {
       }
     }
 
-    const matches = parseOutput(outputToProcess)
+    const matches = parseOutput(outputToProcess, options.outputMode === "files_with_matches")
     const limited = options.headLimit && options.headLimit > 0
       ? matches.slice(0, options.headLimit)
       : matches
diff --git a/src/tools/grep/tools.ts b/src/tools/grep/tools.ts
index 356eb53a4..e4d0e0e42 100644
--- a/src/tools/grep/tools.ts
+++ b/src/tools/grep/tools.ts
@@ -22,7 +22,7 @@ export function createGrepTools(ctx: PluginInput): Record<string, ToolDefinition
         .optional()
         .describe("The directory to search in. Defaults to the current working directory."),
       output_mode: tool.schema
-        .string()
+        .enum(["content", "files_with_matches", "count"])
         .optional()
         .describe(
           "Output mode: \"content\" shows matching lines, \"files_with_matches\" shows only file paths (default), \"count\" shows match counts per file."
@@ -37,7 +37,7 @@ export function createGrepTools(ctx: PluginInput): Record<string, ToolDefinition
         const globs = args.include ? [args.include] : undefined
         const searchPath = args.path ?? ctx.directory
         const paths = [searchPath]
-        const outputMode = (args.output_mode as "content" | "files_with_matches" | "count") ?? "files_with_matches"
+        const outputMode = args.output_mode ?? "files_with_matches"
         const headLimit = args.head_limit ?? 0
 
         if (outputMode === "count") {