diff --git a/README.md b/README.md
index 3eb20e6..ed72e04 100644
--- a/README.md
+++ b/README.md
@@ -83,6 +83,28 @@ alone: the flag only surfaces a per-install opt-in, off by default, next to that
 warning. Set it when the plugin genuinely does not function otherwise, not when
 it merely has a nicer HUD if you do.
 
+### Plugins that ship workshop addons
+
+CS2 cannot send files from a server to a player, so a plugin's custom models,
+sounds, particles or Panorama layouts have to reach players as a Steam Workshop
+addon. A plugin that needs one lists the workshop ids:
+
+```json
+"workshop_addons": ["3791548068"]
+```
+
+5Stack's SwiftlyS2 image ships
+[AddonsManager](https://github.com/SwiftlyS2-Plugins/AddonsManager), so nothing
+else has to be installed: every server that loads the plugin turns it on and
+serves exactly the addons its plugins list. Players download them while they
+connect, and the server fetches each addon again whenever it mounts it, so a
+republished addon reaches players without a new plugin release.
+
+The ids are strings, because a workshop id is too large for a JSON number. The
+entry needs a `swiftlys2` variant, since the SwiftlyS2 image is the only one
+with AddonsManager. A CounterStrikeSharp server loading the same plugin starts
+without the addons and logs why.
+
 ### Plugins that run a map rotation
 
 A dedicated server can carry a map rotation set in the panel. A plugin that can
diff --git a/schema/plugin.schema.json b/schema/plugin.schema.json
index 53e4d1f..a8cdc0b 100644
--- a/schema/plugin.schema.json
+++ b/schema/plugin.schema.json
@@ -69,6 +69,15 @@
       "default": false,
       "description": "Needs FollowCS2ServerGuidelines set to false to work at all. The panel hides the plugin's functionality behind a per-install opt-in and warns that Valve can ban every GSLT on the operator's account."
     },
+    "workshop_addons": {
+      "type": "array",
+      "uniqueItems": true,
+      "items": {
+        "type": "string",
+        "pattern": "^[0-9]+$"
+      },
+      "description": "Steam Workshop ids of addons the plugin's players need: models, sounds, particles, Panorama layouts. A server loading the plugin turns on the AddonsManager built into 5Stack's SwiftlyS2 image, which has connecting players download them. Strings, not numbers: workshop ids overflow a JSON number."
+    },
     "variants": {
       "type": "object",
       "description": "Per-runtime source of the game plugin. Required when kind is game or bundle.",
diff --git a/scripts/build.test.mjs b/scripts/build.test.mjs
index 72d7d9c..400505b 100644
--- a/scripts/build.test.mjs
+++ b/scripts/build.test.mjs
@@ -5,7 +5,11 @@
 import assert from "node:assert/strict";
 import { selectLinuxAsset } from "./build.mjs";
 import { sameIndex } from "./changed.mjs";
-import { validateConfig, validateMapRotation } from "./validate.mjs";
+import {
+  validateConfig,
+  validateMapRotation,
+  validateWorkshopAddons,
+} from "./validate.mjs";
 
 const glob = (pattern) =>
   new RegExp(
@@ -238,6 +242,55 @@ test("rejects forced cvars that are not console variable names", () => {
   assert.equal(problems.length, 1);
 });
 
+const addonsEntry = (fields) => ({
+  kind: "game",
+  variants: { swiftlys2: { repo: "a/b", asset: "B.zip" } },
+  ...fields,
+});
+
+test("accepts workshop addons on a SwiftlyS2 plugin", () => {
+  const problems = validateWorkshopAddons(
+    addonsEntry({ workshop_addons: ["3791548068", "3070212801"] }),
+    "x.json",
+  );
+  assert.deepEqual(problems, []);
+});
+
+// AddonsManager refuses its whole config over one bad id, so a number that
+// lost precision or a pasted URL is caught before it reaches a server.
+test("rejects a workshop id that is not a string of digits", () => {
+  const problems = validateWorkshopAddons(
+    addonsEntry({
+      workshop_addons: [
+        3791548068,
+        "https://steamcommunity.com/sharedfiles/filedetails/?id=3791548068",
+        "",
+      ],
+    }),
+    "x.json",
+  );
+  assert.equal(problems.length, 3);
+});
+
+test("rejects a workshop id listed twice", () => {
+  const problems = validateWorkshopAddons(
+    addonsEntry({ workshop_addons: ["3791548068", "3791548068"] }),
+    "x.json",
+  );
+  assert.equal(problems.length, 1);
+});
+
+test("rejects workshop addons on a plugin with no SwiftlyS2 build", () => {
+  const problems = validateWorkshopAddons(
+    addonsEntry({
+      variants: { counterstrikesharp: { repo: "a/b", asset: "B.zip" } },
+      workshop_addons: ["3791548068"],
+    }),
+    "x.json",
+  );
+  assert.equal(problems.length, 1);
+});
+
 if (failures > 0) {
   console.error(`\n${failures} test(s) failed`);
   process.exit(1);
diff --git a/scripts/validate.mjs b/scripts/validate.mjs
index c28bfa1..d475383 100644
--- a/scripts/validate.mjs
+++ b/scripts/validate.mjs
@@ -134,6 +134,7 @@ export function validateEntry({ entry, filePath, directory, fileName }) {
   }
 
   problems.push(...validateConfig(entry, filePath));
+  problems.push(...validateWorkshopAddons(entry, filePath));
 
   if (entry.wiring) {
     if (entry.kind === "game") {
@@ -306,6 +307,53 @@ export function validateConfig(entry, filePath) {
   return problems;
 }
 
+const WORKSHOP_ID = /^[0-9]+$/;
+
+// AddonsManager validates its config when it starts, so one id that is not a
+// bare number takes it down on every server running the plugin -- and the
+// addons with it. Each is held to that here instead.
+export function validateWorkshopAddons(entry, filePath) {
+  const problems = [];
+  const fail = (message) => problems.push(`${filePath}: ${message}`);
+  const addons = entry.workshop_addons;
+
+  if (addons === undefined) {
+    return problems;
+  }
+
+  if (!Array.isArray(addons)) {
+    fail(`"workshop_addons" must be a list of workshop ids`);
+    return problems;
+  }
+
+  if (entry.kind === "panel") {
+    fail(`"workshop_addons" only belongs on a game or bundle entry`);
+  }
+
+  // The only AddonsManager 5Stack ships is in the SwiftlyS2 image. A plugin
+  // with no SwiftlyS2 build would list addons no server ever serves.
+  if (!entry.variants?.swiftlys2) {
+    fail(`"workshop_addons" are served by AddonsManager, which 5Stack only ships for SwiftlyS2, so the entry needs a swiftlys2 variant`);
+  }
+
+  const seen = new Set();
+
+  for (const id of addons) {
+    if (typeof id !== "string" || !WORKSHOP_ID.test(id)) {
+      fail(`"workshop_addons" has ${JSON.stringify(id)}; a workshop id is a string of digits, e.g. "3791548068"`);
+      continue;
+    }
+
+    if (seen.has(id)) {
+      fail(`"workshop_addons" lists ${id} more than once`);
+    }
+
+    seen.add(id);
+  }
+
+  return problems;
+}
+
 // The subset of JSON Schema the panel's form understands. A default the form
 // cannot render is a broken editor, so it is held to the same rules.
 export function schemaProblems(schema, value, at) {