diff --git a/src/components/Header/Header.tsx b/src/components/Header/Header.tsx
index 8000c9a..b860089 100644
--- a/src/components/Header/Header.tsx
+++ b/src/components/Header/Header.tsx
@@ -8,6 +8,7 @@ import { $editor } from "../../stores/editor.ts";
 import useComponentVisible from "../../useComponentVisible.ts";
 
 import cs from "./Header.module.css";
+import { getQueryParam } from "../../fsInitializer.ts";
 
 export const Header = () => {
   const { isOpen } = useStore($menu);
@@ -31,41 +32,45 @@ export const Header = () => {
         <button className={cs.headerMenuButton} onClick={toggleMenu}>
           {isOpen ? <VscClose size={16} /> : <VscMenu size={16} />}
         </button>
-        {showFork && (
-          <button
-            className={`${cs.forkButton} ${canFork ? "" : cs.disabledButton}`}
-            title={canFork ? "Fork this Gist" : "You need to be logged in to fork this Gist"}
-            disabled={!canFork}
-            onClick={() => forkGist(openedGist.id)}
-          >
-            <VscRepoForked /> Fork
-          </button>
-        )}
-        {(showSave) && (
-          <button
-            className={`${cs.saveButton} ${canSave ? "" : cs.disabledButton}`}
-            title={canSave ? "Create a Gist" : "You need to be logged in to create a Gist"}
-            disabled={!canSave}
-            onClick={saveGist}
-          >
-            <VscSave /> Create Gist
-          </button>
-        )}
-        {showUpdate && (
-          <button
-            className={`${cs.saveButton} ${canUpdate ? "" : cs.disabledButton}`}
-            title={canUpdate ? "Update Gist" : "No changes to save"}
-            disabled={!canUpdate}
-            onClick={() => {
-              updateGist(openedGist.id);
-            }}
-          >
-            <VscSave /> Save
-          </button>
+        {getQueryParam("embed") !== "1" && (
+          <>
+            {showFork && (
+              <button
+                className={`${cs.forkButton} ${canFork ? "" : cs.disabledButton}`}
+                title={canFork ? "Fork this Gist" : "You need to be logged in to fork this Gist"}
+                disabled={!canFork}
+                onClick={() => forkGist(openedGist.id)}
+              >
+                <VscRepoForked /> Fork
+              </button>
+            )}
+            {showSave && (
+              <button
+                className={`${cs.saveButton} ${canSave ? "" : cs.disabledButton}`}
+                title={canSave ? "Create a Gist" : "You need to be logged in to create a Gist"}
+                disabled={!canSave}
+                onClick={saveGist}
+              >
+                <VscSave /> Create Gist
+              </button>
+            )}
+            {showUpdate && (
+              <button
+                className={`${cs.saveButton} ${canUpdate ? "" : cs.disabledButton}`}
+                title={canUpdate ? "Update Gist" : "No changes to save"}
+                disabled={!canUpdate}
+                onClick={() => {
+                  updateGist(openedGist.id);
+                }}
+              >
+                <VscSave /> Save
+              </button>
+            )}
+            <div className={cs.gistLoading}>
+              {gistLoading && <VscLoading size={20} />}
+            </div>
+          </>
         )}
-        <div className={cs.gistLoading}>
-          {gistLoading && <VscLoading size={20} />}
-        </div>
       </div>
 
       <div className={cs.logoContainer}>
@@ -74,32 +79,36 @@ export const Header = () => {
       </div>
 
       <div className={cs.links}>
-        {currentUser.id ? (
-          <div className={cs.userContainer}
-               onClick={() => setIsComponentVisible(true)}
-               ref={ref}
-          >
-            <img className={cs.avatar} src={currentUser.avatarUrl} alt={currentUser.username} />
-            <div className={`${cs.userMenu} ${isComponentVisible ? cs.show : ""}`}>
-              <button className={cs.signOutButton} onClick={signOut}>Sign out</button>
-            </div>
-          </div>
-        ) : (
-          <button className={cs.SignInButton} onClick={() => {
-            const bc = new BroadcastChannel("oauth");
-            bc.onmessage = (event) => {
-              const searchParams = new URLSearchParams(event.data);
-              if (searchParams.get("state") === state) {
-                $oauth.setKey("code", searchParams.get("code") || undefined);
-                $oauth.setKey("error", searchParams.get("error") || undefined);
-                bc.close();
-              }
-              bc.close();
-            };
-            window.open(`https://github.com/login/oauth/authorize?client_id=${import.meta.env.VITE_GITHUB_CLIENT_ID}&scope=gist&state=${state}`, "popup", "popup=true, width=600, height=400");
-          }}>
-            <VscGithub size={16} /> Sign in
-          </button>
+        {getQueryParam("embed") === "1" && (
+          <>
+            {currentUser.id ? (
+              <div className={cs.userContainer}
+                   onClick={() => setIsComponentVisible(true)}
+                   ref={ref}
+              >
+                <img className={cs.avatar} src={currentUser.avatarUrl} alt={currentUser.username} />
+                <div className={`${cs.userMenu} ${isComponentVisible ? cs.show : ""}`}>
+                  <button className={cs.signOutButton} onClick={signOut}>Sign out</button>
+                </div>
+              </div>
+            ) : (
+              <button className={cs.SignInButton} onClick={() => {
+                const bc = new BroadcastChannel("oauth");
+                bc.onmessage = (event) => {
+                  const searchParams = new URLSearchParams(event.data);
+                  if (searchParams.get("state") === state) {
+                    $oauth.setKey("code", searchParams.get("code") || undefined);
+                    $oauth.setKey("error", searchParams.get("error") || undefined);
+                    bc.close();
+                  }
+                  bc.close();
+                };
+                window.open(`https://github.com/login/oauth/authorize?client_id=${import.meta.env.VITE_GITHUB_CLIENT_ID}&scope=gist&state=${state}`, "popup", "popup=true, width=600, height=400");
+              }}>
+                <VscGithub size={16} /> Sign in
+              </button>
+            )}
+          </>
         )}
       </div>
     </header>
diff --git a/src/components/Output/SettingsTab.tsx b/src/components/Output/SettingsTab.tsx
index a0493b0..904ed4d 100644
--- a/src/components/Output/SettingsTab.tsx
+++ b/src/components/Output/SettingsTab.tsx
@@ -15,7 +15,7 @@ function findDirectory(dir: DirectoryContents, s: string) {
   let current = dir;
   for (const part of parts) {
 
-    if (!("contents" in current[part])) {
+    if (!(current[part] && "contents" in current[part])) {
       return undefined;
     }
     current = (current[part] as MarshaledDirectory).contents;
diff --git a/src/fsInitializer.ts b/src/fsInitializer.ts
index 9489333..0a962a3 100644
--- a/src/fsInitializer.ts
+++ b/src/fsInitializer.ts
@@ -1,11 +1,28 @@
 import importFromGist from "./gist.ts";
 
+export const getQueryParam = (key: string) => {
+  const url = new URL(window.location.href);
+  const params = new URLSearchParams(url.search);
+  return params.get(key);
+};
+
 const defaultGem = "octokit";
 
-const mainRbHeader = (gem: string | null) => `# This is a Ruby WASI playground
+const description = `# This is a Ruby WASI playground
 # You can run any Ruby code here and see the result
-# You can also install gems using a Gemfile and the "Bundle install" button.
-${gem ? `\nrequire "${gem}"\n` : ""}`;
+# You can also install gems using a Gemfile and the "Bundle install" button.`;
+
+const mainRbHeader = (gem: string | null) => {
+  const strings: string[] = [];
+  if (getQueryParam("embed") !== "1") {
+    strings.push(description);
+  }
+  if (gem) {
+    strings.push(`require "${gem.split("@")[0]}"\n`);
+  }
+
+  return strings.join("\n");
+};
 
 const mainRb = `${mainRbHeader(defaultGem)}
 # RunRuby.dev comes with a WASI-compatible Faraday adapter
@@ -21,26 +38,20 @@ user = client.user("matz")
 pp({login: user.login, name: user.name, company: user.company})
 `;
 
-export const getQueryParam = (key: string) => {
-  const url = new URL(window.location.href);
-  const params = new URLSearchParams(url.search);
-  return params.get(key);
-};
-
 const gemfileContents = (gem: string) => (
   `source "https://rubygems.org"
 
-gem "${gem}"
+gem "${gem.split("@")[0]}", "${gem.split("@")[1] || ">= 0"}"
 `
 );
 
 const buildStarter = ({ gem, main }: { gem: string | null, main: string }) => {
   const result = [
-    { filename: "main.rb", content: main },
+    { filename: "main.rb", content: main }
   ];
 
   if (gem) {
-    result.push({ filename: "Gemfile", content: gemfileContents(gem) })
+    result.push({ filename: "Gemfile", content: gemfileContents(gem) });
   }
 
   return result;
@@ -62,6 +73,10 @@ export const composeInitialFS = async () => {
   return buildMainRB();
 };
 
+export const urlSafeAtob = (str: string) => {
+  return decodeURIComponent(atob(str.replace(/-/g, "+").replace(/_/g, "/")));
+};
+
 const buildMainRB = () => {
   const initialGem = getQueryParam("gem");
   const initialCode = getQueryParam("code");
@@ -70,7 +85,7 @@ const buildMainRB = () => {
     return { files: buildStarter({ gem: defaultGem, main: mainRb }) };
   }
 
-  const code = initialCode ? decodeURIComponent(atob(initialCode)) : "";
+  const code = initialCode ? urlSafeAtob(initialCode) : "";
   const main = mainRbHeader(initialGem) + "\n" + code;
 
   return { files: buildStarter({ gem: initialGem, main }) };
diff --git a/src/stores/theme.ts b/src/stores/theme.ts
index 5290db5..9cd81a3 100644
--- a/src/stores/theme.ts
+++ b/src/stores/theme.ts
@@ -7,7 +7,6 @@ const THEME_KEY = "theme";
 export const $theme = atom<Theme>("system");
 
 export const setTheme = action($theme, "set", (store, theme: Theme) => {
-
   document.documentElement.setAttribute(THEME_KEY, theme);
   store.set(theme);
   localStorage.setItem(THEME_KEY, theme);