diff --git a/src/commands/fetch.ts b/src/commands/fetch.ts
index 73ce73e..4210ad1 100644
--- a/src/commands/fetch.ts
+++ b/src/commands/fetch.ts
@@ -110,20 +110,27 @@ async function fetchRepoInput(spec: string, cwd: string): Promise<FetchResult> {
   }
 
   const displayName = `${repoSpec.host}/${repoSpec.owner}/${repoSpec.repo}`;
-  console.log(
-    `\nFetching ${repoSpec.owner}/${repoSpec.repo} from ${repoSpec.host}...`,
-  );
+  const displayNameWithSubpath = repoSpec.subpath
+    ? `${displayName}/${repoSpec.subpath}`
+    : displayName;
+  const logTarget = repoSpec.subpath
+    ? `${repoSpec.owner}/${repoSpec.repo}/${repoSpec.subpath}`
+    : `${repoSpec.owner}/${repoSpec.repo}`;
+  console.log(`\nFetching ${logTarget} from ${repoSpec.host}...`);
 
   try {
     // Check if already exists with the same ref
     if (repoExists(displayName, cwd)) {
-      const existing = await getRepoInfo(displayName, cwd);
+      const existing = await getRepoInfo(displayNameWithSubpath, cwd);
       if (existing && repoSpec.ref && existing.version === repoSpec.ref) {
         console.log(`  ✓ Already up to date (${repoSpec.ref})`);
+        const relativePath = repoSpec.subpath
+          ? `${getRepoRelativePath(displayName)}/${repoSpec.subpath}`
+          : getRepoRelativePath(displayName);
         return {
-          package: displayName,
+          package: displayNameWithSubpath,
           version: existing.version,
-          path: getRepoRelativePath(displayName),
+          path: relativePath,
           success: true,
         };
       } else if (existing) {
@@ -140,7 +147,10 @@ async function fetchRepoInput(spec: string, cwd: string): Promise<FetchResult> {
     console.log(`  → Ref: ${resolved.ref}`);
 
     // Fetch the source
-    console.log(`  → Cloning at ${resolved.ref}...`);
+    const cloneMsg = resolved.subpath
+      ? `  → Sparse cloning ${resolved.subpath} at ${resolved.ref}...`
+      : `  → Cloning at ${resolved.ref}...`;
+    console.log(cloneMsg);
     const result = await fetchRepoSource(resolved, cwd);
 
     if (result.success) {
@@ -157,7 +167,7 @@ async function fetchRepoInput(spec: string, cwd: string): Promise<FetchResult> {
     const errorMessage = err instanceof Error ? err.message : String(err);
     console.log(`  ✗ Error: ${errorMessage}`);
     return {
-      package: displayName,
+      package: displayNameWithSubpath,
       version: "",
       path: "",
       success: false,
diff --git a/src/lib/git.ts b/src/lib/git.ts
index 39f1dfe..7533a63 100644
--- a/src/lib/git.ts
+++ b/src/lib/git.ts
@@ -255,6 +255,35 @@ async function cloneAtRef(
   }
 }
 
+/**
+ * Clone with sparse checkout - fetches only the specified subpath
+ */
+async function cloneAtRefSparse(
+  git: SimpleGit,
+  repoUrl: string,
+  targetPath: string,
+  ref: string,
+  subpath: string,
+): Promise<{ success: boolean; ref?: string; error?: string }> {
+  try {
+    await git.clone(repoUrl, targetPath, [
+      "--filter=blob:none",
+      "--sparse",
+      "--branch",
+      ref,
+      "--single-branch",
+    ]);
+    const repoGit = simpleGit(targetPath);
+    await repoGit.raw(["sparse-checkout", "set", subpath]);
+    return { success: true, ref };
+  } catch (err) {
+    return {
+      success: false,
+      error: `Failed to sparse clone: ${err instanceof Error ? err.message : String(err)}`,
+    };
+  }
+}
+
 /**
  * Fetch source code for a resolved package
  */
@@ -364,17 +393,22 @@ export async function fetchRepoSource(
     await mkdir(parentDir, { recursive: true });
   }
 
-  // Clone the repository
-  const cloneResult = await cloneAtRef(
-    git,
-    resolved.repoUrl,
-    repoPath,
-    resolved.ref,
-  );
+  const cloneResult = resolved.subpath
+    ? await cloneAtRefSparse(
+        git,
+        resolved.repoUrl,
+        repoPath,
+        resolved.ref,
+        resolved.subpath,
+      )
+    : await cloneAtRef(git, resolved.repoUrl, repoPath, resolved.ref);
 
   if (!cloneResult.success) {
+    const displayName = resolved.subpath
+      ? `${resolved.displayName}/${resolved.subpath}`
+      : resolved.displayName;
     return {
-      package: resolved.displayName,
+      package: displayName,
       version: resolved.ref,
       path: getRepoRelativePath(resolved.displayName),
       success: false,
@@ -388,10 +422,17 @@ export async function fetchRepoSource(
     await rm(gitDir, { recursive: true, force: true });
   }
 
+  const displayName = resolved.subpath
+    ? `${resolved.displayName}/${resolved.subpath}`
+    : resolved.displayName;
+  const relativePath = resolved.subpath
+    ? `${getRepoRelativePath(resolved.displayName)}/${resolved.subpath}`
+    : getRepoRelativePath(resolved.displayName);
+
   return {
-    package: resolved.displayName,
+    package: displayName,
     version: resolved.ref,
-    path: getRepoRelativePath(resolved.displayName),
+    path: relativePath,
     success: true,
     error: cloneResult.error,
   };
diff --git a/src/lib/registries/index.test.ts b/src/lib/registries/index.test.ts
index 8035182..7e398ae 100644
--- a/src/lib/registries/index.test.ts
+++ b/src/lib/registries/index.test.ts
@@ -232,5 +232,9 @@ describe("detectInputType", () => {
     it("GitLab URL", () => {
       expect(detectInputType("https://gitlab.com/owner/repo")).toBe("repo");
     });
+
+    it("owner/repo/subpath (monorepo subdirectory)", () => {
+      expect(detectInputType("vercel/ai/packages/ai")).toBe("repo");
+    });
   });
 });
diff --git a/src/lib/repo.test.ts b/src/lib/repo.test.ts
index 41582f2..5ebe3fd 100644
--- a/src/lib/repo.test.ts
+++ b/src/lib/repo.test.ts
@@ -15,6 +15,7 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "next.js",
         ref: undefined,
+        subpath: undefined,
       });
     });
 
@@ -25,6 +26,7 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "next.js",
         ref: "v14.0.0",
+        subpath: undefined,
       });
     });
 
@@ -35,6 +37,7 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "next.js",
         ref: "main",
+        subpath: undefined,
       });
     });
   });
@@ -47,6 +50,7 @@ describe("parseRepoSpec", () => {
         owner: "gitlab-org",
         repo: "gitlab",
         ref: undefined,
+        subpath: undefined,
       });
     });
 
@@ -57,6 +61,7 @@ describe("parseRepoSpec", () => {
         owner: "gitlab-org",
         repo: "gitlab",
         ref: "v16.0.0",
+        subpath: undefined,
       });
     });
   });
@@ -69,6 +74,7 @@ describe("parseRepoSpec", () => {
         owner: "atlassian",
         repo: "python-bitbucket",
         ref: undefined,
+        subpath: undefined,
       });
     });
   });
@@ -81,6 +87,7 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "ai",
         ref: undefined,
+        subpath: undefined,
       });
     });
 
@@ -91,6 +98,7 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "ai",
         ref: undefined,
+        subpath: undefined,
       });
     });
 
@@ -101,6 +109,31 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "ai",
         ref: "canary",
+        subpath: undefined,
+      });
+    });
+
+    it("parses https://github.com/owner/repo/tree/branch/subpath", () => {
+      const result = parseRepoSpec(
+        "https://github.com/vercel/ai/tree/main/packages/ai",
+      );
+      expect(result).toEqual({
+        host: "github.com",
+        owner: "vercel",
+        repo: "ai",
+        ref: "main",
+        subpath: "packages/ai",
+      });
+    });
+
+    it("parses https://github.com/owner/repo with subpath (no tree)", () => {
+      const result = parseRepoSpec("https://github.com/vercel/ai/packages/ai");
+      expect(result).toEqual({
+        host: "github.com",
+        owner: "vercel",
+        repo: "ai",
+        ref: undefined,
+        subpath: "packages/ai",
       });
     });
 
@@ -111,6 +144,7 @@ describe("parseRepoSpec", () => {
         owner: "gitlab-org",
         repo: "gitlab",
         ref: undefined,
+        subpath: undefined,
       });
     });
 
@@ -121,6 +155,7 @@ describe("parseRepoSpec", () => {
         owner: "owner",
         repo: "repo",
         ref: undefined,
+        subpath: undefined,
       });
     });
   });
@@ -133,6 +168,18 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "next.js",
         ref: undefined,
+        subpath: undefined,
+      });
+    });
+
+    it("parses github.com/owner/repo/subpath", () => {
+      const result = parseRepoSpec("github.com/vercel/ai/packages/ai");
+      expect(result).toEqual({
+        host: "github.com",
+        owner: "vercel",
+        repo: "ai",
+        ref: undefined,
+        subpath: "packages/ai",
       });
     });
 
@@ -143,6 +190,7 @@ describe("parseRepoSpec", () => {
         owner: "gitlab-org",
         repo: "gitlab",
         ref: undefined,
+        subpath: undefined,
       });
     });
   });
@@ -155,6 +203,7 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "next.js",
         ref: undefined,
+        subpath: undefined,
       });
     });
 
@@ -165,6 +214,7 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "next.js",
         ref: "v14.0.0",
+        subpath: undefined,
       });
     });
 
@@ -175,6 +225,51 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "ai",
         ref: "main",
+        subpath: undefined,
+      });
+    });
+
+    it("parses owner/repo/subpath (monorepo subdirectory)", () => {
+      const result = parseRepoSpec("vercel/ai/packages/ai");
+      expect(result).toEqual({
+        host: "github.com",
+        owner: "vercel",
+        repo: "ai",
+        ref: undefined,
+        subpath: "packages/ai",
+      });
+    });
+
+    it("parses owner/repo/subpath with ref", () => {
+      const result = parseRepoSpec("vercel/ai/packages/ai@main");
+      expect(result).toEqual({
+        host: "github.com",
+        owner: "vercel",
+        repo: "ai",
+        ref: "main",
+        subpath: "packages/ai",
+      });
+    });
+
+    it("parses owner/repo/nested/subpath", () => {
+      const result = parseRepoSpec("facebook/react/packages/react");
+      expect(result).toEqual({
+        host: "github.com",
+        owner: "facebook",
+        repo: "react",
+        ref: undefined,
+        subpath: "packages/react",
+      });
+    });
+
+    it("parses github:owner/repo/subpath", () => {
+      const result = parseRepoSpec("github:vercel/ai/packages/ai");
+      expect(result).toEqual({
+        host: "github.com",
+        owner: "vercel",
+        repo: "ai",
+        ref: undefined,
+        subpath: "packages/ai",
       });
     });
 
@@ -185,6 +280,7 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "next.js",
         ref: undefined,
+        subpath: undefined,
       });
     });
 
@@ -195,6 +291,7 @@ describe("parseRepoSpec", () => {
         owner: "facebook",
         repo: "react-native",
         ref: undefined,
+        subpath: undefined,
       });
     });
   });
@@ -224,6 +321,7 @@ describe("parseRepoSpec", () => {
         owner: "vercel",
         repo: "ai",
         ref: undefined,
+        subpath: undefined,
       });
     });
   });
@@ -269,6 +367,11 @@ describe("isRepoSpec", () => {
       expect(isRepoSpec("vercel/ai@main")).toBe(true);
       expect(isRepoSpec("vercel/ai#canary")).toBe(true);
     });
+
+    it("owner/repo/subpath (monorepo subdirectory)", () => {
+      expect(isRepoSpec("vercel/ai/packages/ai")).toBe(true);
+      expect(isRepoSpec("facebook/react/packages/react")).toBe(true);
+    });
   });
 
   describe("returns false for non-repo specs", () => {
diff --git a/src/lib/repo.ts b/src/lib/repo.ts
index b4e6f81..05bdf0f 100644
--- a/src/lib/repo.ts
+++ b/src/lib/repo.ts
@@ -53,15 +53,22 @@ export function parseRepoSpec(spec: string): RepoSpec | null {
         repo = repo.slice(0, -4);
       }
 
+      let subpath: string | undefined;
+
       // Handle /tree/branch or /blob/branch URLs
       if (
         pathParts.length >= 4 &&
         (pathParts[2] === "tree" || pathParts[2] === "blob")
       ) {
         ref = pathParts[3];
+        if (pathParts.length > 4) {
+          subpath = pathParts.slice(4).join("/");
+        }
+      } else if (pathParts.length > 2) {
+        subpath = pathParts.slice(2).join("/");
       }
 
-      return { host, owner, repo, ref };
+      return { host, owner, repo, ref, subpath };
     } catch {
       return null;
     }
@@ -76,13 +83,13 @@ export function parseRepoSpec(spec: string): RepoSpec | null {
   else if (input.startsWith("@")) {
     return null;
   }
-  // Must contain exactly one / to be a repo (owner/repo)
-  else if (input.split("/").length !== 2) {
+  // Must contain at least owner/repo (2 segments)
+  else if (input.split("/").length < 2) {
     return null;
   }
 
   // Extract ref from @ or # suffix
-  // owner/repo@v1.0.0 or owner/repo#main
+  // owner/repo@v1.0.0 or owner/repo#main or owner/repo/path@main
   const atIndex = input.indexOf("@");
   const hashIndex = input.indexOf("#");
 
@@ -94,17 +101,21 @@ export function parseRepoSpec(spec: string): RepoSpec | null {
     input = input.slice(0, hashIndex);
   }
 
-  // Split into owner/repo
+  // Split into owner/repo[/subpath]
   const parts = input.split("/");
-  if (parts.length !== 2 || !parts[0] || !parts[1]) {
+  if (parts.length < 2 || !parts[0] || !parts[1]) {
     return null;
   }
 
+  const subpath =
+    parts.length > 2 ? parts.slice(2).join("/") : undefined;
+
   return {
     host,
     owner: parts[0],
     repo: parts[1],
     ref,
+    subpath,
   };
 }
 
@@ -138,16 +149,14 @@ export function isRepoSpec(spec: string): boolean {
     return false;
   }
 
-  // owner/repo format (must have exactly one /)
-  // But need to distinguish from things that aren't repos
-  const parts = trimmed.split("/");
-  if (parts.length === 2 && parts[0] && parts[1]) {
-    // Extract the repo part (before any @ or #)
-    const repoPart = parts[1].split("@")[0].split("#")[0];
+  // owner/repo or owner/repo/subpath format (2+ segments)
+  const pathPart = trimmed.split("@")[0].split("#")[0];
+  const parts = pathPart.split("/");
+  if (parts.length >= 2 && parts[0] && parts[1]) {
     // Valid usernames and repos: alphanumeric, hyphens, underscores
     // Repos can also have dots
     const validOwner = /^[a-zA-Z0-9][a-zA-Z0-9-]*$/.test(parts[0]);
-    const validRepo = /^[a-zA-Z0-9._-]+$/.test(repoPart);
+    const validRepo = /^[a-zA-Z0-9._-]+$/.test(parts[1]);
     return validOwner && validRepo;
   }
 
@@ -170,12 +179,12 @@ interface GitLabApiResponse {
  * Resolve a repo spec to full repository information using the appropriate API
  */
 export async function resolveRepo(spec: RepoSpec): Promise<ResolvedRepo> {
-  const { host, owner, repo, ref } = spec;
+  const { host, owner, repo, ref, subpath } = spec;
 
   if (host === "github.com") {
-    return resolveGitHubRepo(host, owner, repo, ref);
+    return resolveGitHubRepo(host, owner, repo, ref, subpath);
   } else if (host === "gitlab.com") {
-    return resolveGitLabRepo(host, owner, repo, ref);
+    return resolveGitLabRepo(host, owner, repo, ref, subpath);
   } else {
     // For unsupported hosts, assume default branch is "main"
     return {
@@ -185,6 +194,7 @@ export async function resolveRepo(spec: RepoSpec): Promise<ResolvedRepo> {
       ref: ref || "main",
       repoUrl: `https://${host}/${owner}/${repo}`,
       displayName: `${host}/${owner}/${repo}`,
+      subpath,
     };
   }
 }
@@ -194,6 +204,7 @@ async function resolveGitHubRepo(
   owner: string,
   repo: string,
   ref?: string,
+  subpath?: string,
 ): Promise<ResolvedRepo> {
   const apiUrl = `https://api.github.com/repos/${owner}/${repo}`;
 
@@ -231,6 +242,7 @@ async function resolveGitHubRepo(
     ref: resolvedRef,
     repoUrl: `https://github.com/${owner}/${repo}`,
     displayName: `${host}/${owner}/${repo}`,
+    subpath,
   };
 }
 
@@ -239,6 +251,7 @@ async function resolveGitLabRepo(
   owner: string,
   repo: string,
   ref?: string,
+  subpath?: string,
 ): Promise<ResolvedRepo> {
   const projectPath = encodeURIComponent(`${owner}/${repo}`);
   const apiUrl = `https://gitlab.com/api/v4/projects/${projectPath}`;
@@ -271,6 +284,7 @@ async function resolveGitLabRepo(
     ref: resolvedRef,
     repoUrl: `https://gitlab.com/${owner}/${repo}`,
     displayName: `${host}/${owner}/${repo}`,
+    subpath,
   };
 }
 
diff --git a/src/types.ts b/src/types.ts
index 8d0a42a..af566b8 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -60,6 +60,7 @@ export interface RepoSpec {
   owner: string;
   repo: string;
   ref?: string; // branch, tag, or commit
+  subpath?: string; // e.g., "packages/ai" for monorepo subdirectory
 }
 
 /**
@@ -86,4 +87,5 @@ export interface ResolvedRepo {
   ref: string; // branch, tag, or commit (resolved)
   repoUrl: string;
   displayName: string; // e.g., "github.com/owner/repo"
+  subpath?: string; // e.g., "packages/ai" for monorepo subdirectory
 }