diff --git a/TODO.md b/TODO.md
index baff0324..410089b7 100644
--- a/TODO.md
+++ b/TODO.md
@@ -22,7 +22,7 @@ the owner's OS user and can never be granted. Indirection there really is accide
 
 ## Themes
 
-**107 open, 32 closed**, across 34 themes.
+**106 open, 33 closed**, across 34 themes.
 
 | Theme | Open | Closed |
 | --- | --- | --- |
@@ -45,7 +45,7 @@ the owner's OS user and can never be granted. Indirection there really is accide
 | [Mobile apps](todo/mobile-apps/) | 5 | 0 |
 | [Multi-user](todo/multi-user/) | 17 | 5 |
 | [Notifications](todo/notifications/) | 1 | 0 |
-| [Plugin ecosystem — before it opens to third parties (2026-08-18)](todo/plugin-ecosystem/) | 5 | 0 |
+| [Plugin ecosystem — before it opens to third parties (2026-08-18)](todo/plugin-ecosystem/) | 4 | 1 |
 | [Plugin infrastructure](todo/plugin-infrastructure/) | 2 | 1 |
 | [Plugin repos — what writing their READMEs turned up](todo/plugin-repos/) | 10 | 9 |
 | [Plugin system — gaps the email extraction found (2026-08-18)](todo/plugin-system/) | 3 | 0 |
diff --git a/src/servers/api/plugins/router.ts b/src/servers/api/plugins/router.ts
index c01660f3..37f89e08 100644
--- a/src/servers/api/plugins/router.ts
+++ b/src/servers/api/plugins/router.ts
@@ -224,6 +224,58 @@ pluginsRouter.post('/update-all', async (ctx) => {
   });
 });
 
+/*
+  POST /plugins/install-from-url — a plugin that is in no registry.
+
+  The catalogue was the only way a remote plugin could arrive, so "build one and give it to a friend"
+  had no route at all. The first real case is a plugin that must never be listed: fofos-admin is one
+  website's admin panel, useful to exactly one person, and putting it in a public registry to install it
+  would be the wrong shape.
+
+  ── The name comes from the URL, because the name IS the directory ──
+
+  `appName` is taken from the directory a plugin sits in and never declared in its manifest, so the id
+  cannot disagree with where the code is. That decision is made for us here: the repository name becomes
+  the directory, and therefore the id, the route segment, the table prefix and the sidecar suffix. A
+  repository called something unusable as an id is refused before anything is cloned rather than after —
+  a half-clone under a bad name is a plugin the platform reports as broken instead of absent.
+
+  ── Owner-only, and it is not the same owner-only as the rest of this router ──
+
+  Every route here is owner-gated because installing a plugin mounts routes and starts a process. This
+  one also takes an ADDRESS from the caller, so the owner is choosing what code runs, not choosing from
+  a catalogue somebody curated. The URL is validated in `fetch.ts` — https, no credentials, no shell —
+  but validation is not review: nothing here reads what it cloned.
+*/
+pluginsRouter.post('/install-from-url', async (ctx) => {
+  type FromUrl = { url?: string; appName?: string };
+  const body = await ctx.req.json<FromUrl>().catch(() => ({}) as FromUrl);
+  const url = body.url?.trim();
+  if (!url) throw errors.BAD_REQUEST('url is required');
+
+  // `https://host/owner/repo` or `…/repo.git` → `repo`. Derived rather than asked for, so the name and
+  // the address cannot disagree; `appName` in the body only OVERRIDES it, for a repository whose name is
+  // not the id you want.
+  const derived = url
+    .replace(/\.git$/, '')
+    .replace(/\/+$/, '')
+    .split('/')
+    .pop();
+  const appName = body.appName?.trim() || derived;
+
+  // The same shape every other plugin id has. Checked here because everything downstream — the route
+  // segment, the table prefix, the pm2 process name — inherits it, and each of those fails differently.
+  if (!appName || !/^[a-z0-9]+(-[a-z0-9]+)*$/.test(appName)) {
+    throw errors.BAD_REQUEST(
+      `"${appName ?? ''}" is not a usable plugin name. Lowercase letters, digits and single hyphens — ` +
+        'it becomes the directory, the route and the table prefix.',
+    );
+  }
+
+  const result = await installPlugin(appName, undefined, ctx.get('user').id, undefined, url);
+  return ctx.json(result, result.ok ? 200 : 400);
+});
+
 pluginsRouter.post('/:appName/install', async (ctx) => {
   const result = await installPlugin(ctx.req.param('appName'), undefined, ctx.get('user').id);
   return ctx.json(result, result.ok ? 200 : 400);
diff --git a/src/servers/plugins/fetch.ts b/src/servers/plugins/fetch.ts
index e91306a9..a337125e 100644
--- a/src/servers/plugins/fetch.ts
+++ b/src/servers/plugins/fetch.ts
@@ -40,7 +40,7 @@ const gitAvailable = (): boolean => !!Bun.which('git');
  * verb with different questions — what happens to uncommitted changes, does the version go backwards —
  * and it does not exist yet.
  */
-export async function fetchPlugin(appName: string, onLog?: OnLog): Promise<FetchResult> {
+export async function fetchPlugin(appName: string, onLog?: OnLog, source?: string): Promise<FetchResult> {
   const dir = join(PLUGINS_DIR, appName);
 
   if (existsSync(dir)) {
@@ -50,8 +50,20 @@ export async function fetchPlugin(appName: string, onLog?: OnLog): Promise<Fetch
     return { ok: false, dir, error: 'git is not installed on this machine' };
   }
 
-  const entry = await catalogueEntry(appName);
-  if (!entry) return { ok: false, dir, error: `no catalogue entry for "${appName}"` };
+  /*
+    A URL the caller supplied, or the catalogue's.
+
+    The catalogue is not the only way a plugin should be able to arrive. "Build one and give it to a
+    friend" had no route at all, and the first real case is a plugin that must NOT be listed: fofos-admin
+    is one website's admin panel and belongs in nobody's registry.
+
+    The URL is checked identically either way, below. It has to be — the catalogue is not a trust
+    boundary here, it is just where a string came from, and the same string reaches the same command
+    line. What DOES differ is who is asking: an install from a URL is somebody typing an address, so the
+    route that accepts one is owner-only.
+  */
+  const url = source?.trim() || (await catalogueEntry(appName))?.source;
+  if (!url) return { ok: false, dir, error: `no catalogue entry for "${appName}", and no source URL given` };
 
   // The URL comes from the catalogue and reaches a command line, so it is checked rather than trusted.
   // Deliberately narrow: https only, no credentials in the URL, no shell metacharacters. A private
@@ -63,8 +75,8 @@ export async function fetchPlugin(appName: string, onLog?: OnLog): Promise<Fetch
   // refused a completely valid, credential-free, https clone URL with a message ("https URLs only, no
   // credentials") that describes neither actual reason. Row fixed for consistency with its siblings, but
   // the regex should never have depended on it.
-  if (!/^https:\/\/[A-Za-z0-9._~\-/]+(\.git)?$/.test(entry.source)) {
-    return { ok: false, dir, error: `refusing to clone from "${entry.source}" — https URLs only, no credentials` };
+  if (!/^https:\/\/[A-Za-z0-9._~\-/]+(\.git)?$/.test(url)) {
+    return { ok: false, dir, error: `refusing to clone from "${url}" — https URLs only, no credentials` };
   }
 
   const result = await runLogged(
@@ -74,7 +86,7 @@ export async function fetchPlugin(appName: string, onLog?: OnLog): Promise<Fetch
     // `--progress` instead of `--quiet`: git only reports progress when it believes it has a terminal, and
     // this is the step where a slow link looks identical to a hang. `runLogged` collapses the per-percent
     // rewrites, so the counter is readable rather than a flood.
-    ['git', 'clone', '--depth', '1', '--progress', entry.source, dir],
+    ['git', 'clone', '--depth', '1', '--progress', url, dir],
     {
       // No terminal to answer a credential prompt: without this, a repository that turned private hangs
       // the install forever rather than failing it. Same reasoning as `sudo -n` in os-deps.ts.
diff --git a/src/servers/plugins/install.ts b/src/servers/plugins/install.ts
index 1c941ee3..8dcfe333 100644
--- a/src/servers/plugins/install.ts
+++ b/src/servers/plugins/install.ts
@@ -145,6 +145,14 @@ export async function installPlugin(
   onStep?: OnStep,
   forUserId?: number,
   onLog?: OnLog,
+  /**
+   * Clone from HERE instead of from the catalogue.
+   *
+   * For a plugin that is not in any registry and should not be — one website's admin panel, something
+   * built for one person. Ignored when the plugin is already on disk, because then there is nothing to
+   * fetch and a URL would be describing a decision already made.
+   */
+  source?: string,
 ): Promise<PluginActionResult> {
   const steps: string[] = [];
 
@@ -160,7 +168,7 @@ export async function installPlugin(
   // as it was.
   let plugin = await findPlugin(appName);
   if (!plugin) {
-    const fetched = await fetchPlugin(appName, onLog);
+    const fetched = await fetchPlugin(appName, onLog, source);
     if (!fetched.ok) {
       return { ok: false, appName, steps, error: fetched.error ?? `cannot fetch "${appName}"` };
     }
diff --git a/todo/plugin-ecosystem/no-install-from-git-url.md b/todo/plugin-ecosystem/no-install-from-git-url.md
index 4fe9dad4..44117e4e 100644
--- a/todo/plugin-ecosystem/no-install-from-git-url.md
+++ b/todo/plugin-ecosystem/no-install-from-git-url.md
@@ -2,7 +2,7 @@
 id: plugin-ecosystem/no-install-from-git-url
 title: "No install-from-git-URL"
 theme: plugin-ecosystem
-status: open
+status: done
 created: 2026-08-18
 date_source: section
 order: 3
@@ -11,3 +11,18 @@ order: 3
 **No install-from-git-URL.** The catalogue is the only route for a remote plugin, so the
 "build your own, give it to a friend" path has no affordance. Small, and needed before the
 unofficial channel is real.
+
+**Done 2026-08-28.** `POST /api/plugins/install-from-url`, owner-only, taking `{ url }` and optionally
+`{ appName }`.
+
+Smaller than this note assumed: `fetchPlugin` already cloned, validated the URL, refused to overwrite an
+existing directory, checked for a `manifest.ts` and cleaned up a failed clone. One line tied it to the
+catalogue — where the URL came from. So the change is a source parameter threaded through, plus a route.
+
+The name comes from the repository, because `appName` IS the directory name and is never declared in a
+manifest. That is checked against `^[a-z0-9]+(-[a-z0-9]+)*$` BEFORE cloning: it becomes the route
+segment, the table prefix and the pm2 process name, and a half-clone under an unusable name reads as a
+broken plugin rather than an absent one.
+
+The first real user is `fofos/fofos-admin` — one website's admin panel, which should never be in a
+registry. Verified end to end against it and then purged, since this is not that website's machine.