diff --git a/src/cli.ts b/src/cli.ts
index 2bb99d0..23bbefc 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -6,6 +6,7 @@ import type { GitRunner } from "./git.ts";
 import { SystemGit } from "./git.ts";
 import {
   exists,
+  findDefaultManifestPath,
   loadManifest,
   manifestPaths,
   resolveRepositoryPath,
@@ -39,7 +40,7 @@ class CliHelp extends Error {}
 interface CliOptions {
   command: string;
   subcommand?: string;
-  manifestPath: string;
+  manifestPath?: string;
   json: boolean;
   stale: boolean;
   dryRun: boolean;
@@ -61,7 +62,7 @@ Usage:
   wspace validate
 
 Options:
-  --manifest <path>  Manifest path (default: repos.json)
+  --manifest <path>  Manifest path (default: wspace.json / workspace.json / repos.json)
   --json             Machine-readable output
   --stale            Filter worktrees fully merged into origin/<default> (or missing branch)
   --dry-run          Preview environment sync operations without modifying files
@@ -93,7 +94,7 @@ function parseCliArgs(args: string[]): CliOptions {
   return {
     command,
     subcommand: positional[1],
-    manifestPath: parsed.manifest ?? "repos.json",
+    manifestPath: parsed.manifest,
     json: parsed.json ?? false,
     stale: parsed.stale ?? false,
     dryRun: parsed["dry-run"] ?? false,
@@ -351,7 +352,9 @@ Required setup steps may include:
 
 export async function run(args: string[]): Promise<number> {
   const opts = parseCliArgs(args);
-  const manifestPath = resolve(Deno.cwd(), opts.manifestPath);
+  const manifestPath = opts.manifestPath
+    ? resolve(Deno.cwd(), opts.manifestPath)
+    : await findDefaultManifestPath();
   const manifest = await loadManifest(manifestPath);
   const paths = manifestPaths(manifest, manifestPath);
   return await runCommand(opts, manifest, paths, new SystemGit());
diff --git a/src/manifest.ts b/src/manifest.ts
index 47497f7..ea4bcf0 100644
--- a/src/manifest.ts
+++ b/src/manifest.ts
@@ -3,6 +3,12 @@ import type { RepositoryEntry, WorkspaceManifest } from "./types.ts";
 
 export const CURRENT_SCHEMA_VERSION = 1;
 
+export const DEFAULT_MANIFEST_FILENAMES = [
+  "wspace.json",
+  "workspace.json",
+  "repos.json",
+];
+
 export interface ManifestPaths {
   root: string;
   repositoriesDirectory: string;
@@ -10,6 +16,18 @@ export interface ManifestPaths {
   vaultDirectory: string;
 }
 
+export async function findDefaultManifestPath(
+  cwd: string = Deno.cwd(),
+): Promise<string> {
+  for (const filename of DEFAULT_MANIFEST_FILENAMES) {
+    const candidate = resolve(cwd, filename);
+    if (await exists(candidate)) {
+      return candidate;
+    }
+  }
+  return resolve(cwd, DEFAULT_MANIFEST_FILENAMES[0]);
+}
+
 export function validateSafeName(name: string, contextName = "Name"): void {
   if (!name || typeof name !== "string" || name.trim() === "") {
     throw new Error(`${contextName} cannot be empty`);
diff --git a/tests/manifest_test.ts b/tests/manifest_test.ts
index 855c0bb..d40de45 100644
--- a/tests/manifest_test.ts
+++ b/tests/manifest_test.ts
@@ -1,6 +1,10 @@
 import { assertEquals, assertThrows } from "@std/assert";
 import { dirname, join } from "@std/path";
-import { manifestPaths, validateManifest } from "../src/manifest.ts";
+import {
+  findDefaultManifestPath,
+  manifestPaths,
+  validateManifest,
+} from "../src/manifest.ts";
 import type { WorkspaceManifest } from "../src/types.ts";
 
 Deno.test("validateManifest accepts a valid manifest", () => {
@@ -80,3 +84,31 @@ Deno.test("validateManifest rejects invalid repo names or traversal", () => {
     "invalid characters or path traversal",
   );
 });
+
+Deno.test("findDefaultManifestPath respects fallback order wspace.json -> workspace.json -> repos.json", async () => {
+  const tempDir = await Deno.makeTempDir();
+  try {
+    // When no manifest exists, defaults to wspace.json
+    assertEquals(
+      await findDefaultManifestPath(tempDir),
+      join(tempDir, "wspace.json"),
+    );
+
+    // If repos.json exists, resolves repos.json
+    const reposPath = join(tempDir, "repos.json");
+    await Deno.writeTextFile(reposPath, "{}");
+    assertEquals(await findDefaultManifestPath(tempDir), reposPath);
+
+    // If workspace.json exists, takes priority over repos.json
+    const workspacePath = join(tempDir, "workspace.json");
+    await Deno.writeTextFile(workspacePath, "{}");
+    assertEquals(await findDefaultManifestPath(tempDir), workspacePath);
+
+    // If wspace.json exists, takes top priority
+    const wspacePath = join(tempDir, "wspace.json");
+    await Deno.writeTextFile(wspacePath, "{}");
+    assertEquals(await findDefaultManifestPath(tempDir), wspacePath);
+  } finally {
+    await Deno.remove(tempDir, { recursive: true });
+  }
+});