diff --git a/tools/manifest/schema.json b/tools/manifest/schema.json
new file mode 100644
index 000000000..d90d14934
--- /dev/null
+++ b/tools/manifest/schema.json
@@ -0,0 +1,57 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Pack Manifest",
+  "description": "Defines a publishable pack in the monorepo",
+  "type": "object",
+  "required": ["id", "name", "type", "loader", "mc_version", "version", "release_type"],
+  "additionalProperties": false,
+  "properties": {
+    "$schema": {
+      "type": "string",
+      "description": "Path to this schema file."
+    },
+    "id": {
+      "type": "string",
+      "description": "Matches the directory name",
+      "minLength": 1
+    },
+    "name": {
+      "type": "string",
+      "description": "Human-readable pack name shown on Modrinth/CurseForge. Ie. Re-Console Plus",
+      "minLength": 1
+    },
+    "type": {
+      "type": "string",
+      "description": "Pack type. 'modpack' exports via packwiz, 'datapack' zips the content directory",
+      "enum": ["modpack", "datapack"]
+    },
+    "loader": {
+      "type": "string",
+      "description": "Mod loader this pack targets (e.g., 'fabric', 'neoforge', 'forge', 'quilt')",
+      "minLength": 1
+    },
+    "mc_version": {
+      "type": "string",
+      "description": "Target Minecraft version (e.g., '1.21.10')",
+      "minLength": 1
+    },
+    "version": {
+      "type": "string",
+      "description": "Pack version.",
+      "minLength": 1
+    },
+    "release_type": {
+      "type": "string",
+      "description": "Release channel",
+      "enum": ["release", "beta", "alpha"]
+    },
+    "modrinth_id": {
+      "type": "string",
+      "description": "Modrinth project ID or slug (e.g., 'legacy-minecraft'). Leave empty if not publishing to Modrinth"
+    },
+    "curseforge_id": {
+      "type": "string",
+      "description": "CurseForge project slug or numeric ID (e.g., 're-console'). Leave empty if not publishing to CurseForge"
+    }
+  }
+}
diff --git a/tools/manifest/validate.ts b/tools/manifest/validate.ts
new file mode 100644
index 000000000..5f7f95e67
--- /dev/null
+++ b/tools/manifest/validate.ts
@@ -0,0 +1,112 @@
+import * as fs from 'fs';
+import * as path from 'path';
+
+interface Manifest {
+  id: string;
+  name: string;
+  type: 'modpack' | 'datapack';
+  loader: string;
+  mc_version: string;
+  version: string;
+  release_type: 'release' | 'beta' | 'alpha';
+  modrinth_id?: string;
+  curseforge_id?: string;
+}
+
+function fail(msg: string): never {
+  console.error(`::error::${msg}`);
+  process.exit(1);
+}
+
+function warn(msg: string): void {
+  console.warn(`::warning::${msg}`);
+}
+
+function validate(manifestPath: string): void {
+  if (!fs.existsSync(manifestPath)) {
+    fail(`manifest not found: ${manifestPath}`);
+  }
+
+  let manifest: Manifest;
+  try {
+    const raw = fs.readFileSync(manifestPath, 'utf-8');
+    manifest = JSON.parse(raw);
+  } catch (e) {
+    fail(`failed to parse ${manifestPath}: ${e instanceof Error ? e.message : e}`);
+  }
+
+  const required = [
+    'id', 'name', 'type', 'loader', 'mc_version', 'version', 'release_type',
+  ] as const;
+  for (const field of required) {
+    const v = manifest[field];
+    if (v === undefined || v === null || v === '') {
+      fail(`manifest missing required field: ${field}`);
+    }
+  }
+
+  if (!['modpack', 'datapack'].includes(manifest.type)) {
+    fail(`invalid 'type': ${manifest.type} (must be 'modpack' or 'datapack')`);
+  }
+  if (!['release', 'beta', 'alpha'].includes(manifest.release_type)) {
+    fail(`invalid 'release_type': ${manifest.release_type} (must be 'release', 'beta', or 'alpha')`);
+  }
+
+  const hasMr = manifest.modrinth_id && manifest.modrinth_id.trim() !== '';
+  const hasCf = manifest.curseforge_id && manifest.curseforge_id.trim() !== '';
+  if (!hasMr && !hasCf) {
+    fail('manifest must set at least one of modrinth_id or curseforge_id');
+  }
+
+  const packDir = path.dirname(manifestPath);
+
+  const changelogPath = path.join(packDir, 'changelog.md');
+  if (!fs.existsSync(changelogPath)) {
+    fail(`changelog.md is missing at ${changelogPath}`);
+  }
+  const changelog = fs.readFileSync(changelogPath, 'utf-8').trim();
+  if (changelog === '') {
+    fail(`changelog.md is empty at ${changelogPath}`);
+  }
+  const contentLines = changelog.split('\n').filter(l => l.trim() && !l.trim().startsWith('#'));
+  if (contentLines.length === 0) {
+    fail(`changelog.md has headers but no content at ${changelogPath}`);
+  }
+
+  if (manifest.type === 'modpack') {
+    const mr = path.join(packDir, `${manifest.mc_version}-mr`);
+    const cf = path.join(packDir, `${manifest.mc_version}-cf`);
+
+    if (hasMr && !fs.existsSync(mr)) {
+      fail(`modrinth_id is set but ${mr} does not exist`);
+    }
+    if (hasCf && !fs.existsSync(cf)) {
+      fail(`curseforge_id is set but ${cf} does not exist`);
+    }
+    if (fs.existsSync(mr) && !hasMr) {
+      warn(`${mr} exists but modrinth_id is not set`);
+    }
+    if (fs.existsSync(cf) && !hasCf) {
+      warn(`${cf} exists but curseforge_id is not set`);
+    }
+  }
+
+  if (manifest.type === 'datapack') {
+    const content = path.join(packDir, 'content');
+    if (!fs.existsSync(content)) {
+      fail(`datapack content directory missing: ${content}`);
+    }
+  }
+
+  console.log(`${manifest.id} ${manifest.version} (${manifest.release_type}) — manifest OK`);
+}
+
+const args = process.argv.slice(2);
+if (args.length === 0) {
+  console.error('usage: tsx validate.ts <path/to/manifest.json> [more manifests...]');
+  process.exit(1);
+}
+
+for (const manifestPath of args) {
+  validate(manifestPath);
+}