diff --git a/packages/flexsearch/index.ts b/packages/flexsearch/index.ts
new file mode 100644
index 000000000..940c01286
--- /dev/null
+++ b/packages/flexsearch/index.ts
@@ -0,0 +1,69 @@
+import Document from 'flexsearch/src/document';
+import * as cjk from 'flexsearch/src/lang/cjk/default';
+import {
+    _, buildProjection, Context, DocumentModel, Logger, SystemModel,
+} from 'hydrooj';
+
+const logger = new Logger('flexsearch');
+
+export async function apply(ctx: Context) {
+    logger.info('Building index...');
+    const index = new Document({
+        ...cjk,
+        tokenize: 'strict',
+        // optimize: true,
+        // resolution: 9,
+        document: {
+            id: 'id',
+            tag: 'domainId',
+            index: [{
+                field: 'title',
+                tokenize: 'full',
+            }],
+        },
+        worker: true,
+    }) as any;
+    const pdocs = await DocumentModel.coll.find({ docType: 10 })
+        .project(buildProjection(['docId', 'pid', 'domainId', 'title']))
+        .toArray();
+    for (const pdoc of pdocs as any[]) {
+        pdoc.id = `${pdoc.domainId}/${pdoc.docId}`;
+        delete pdoc._id;
+        delete pdoc.docId;
+        index.add(pdoc);
+    }
+    logger.success('Index built.');
+    try {
+        await index.searchAsync('a', { tag: 'system', limit: 1 });
+    } catch (e) {
+        logger.error('Failed to perform search operation.');
+        logger.error(e);
+        return;
+    }
+    global.Hydro.lib.problemSearch = async (domainId, query, opts) => {
+        const limit = opts?.limit || SystemModel.get('pagination.problem');
+        const ids = await index.searchAsync(query, { tag: domainId, limit })[0]?.result || [];
+        return {
+            countRelation: 'eq',
+            total: ids.length,
+            hits: ids,
+        };
+    };
+
+    ctx.on('problem/add', async (doc, docId) => {
+        const pdoc = _.pick(doc, ['pid', 'domainId', 'title']) as any;
+        pdoc.id = `${doc.domainId}/${docId}`;
+        index.add(pdoc);
+    });
+
+    ctx.on('problem/edit', async (doc) => {
+        const pdoc = _.pick(doc, ['pid', 'domainId', 'title']) as any;
+        pdoc.id = `${doc.domainId}/${doc.docId}`;
+        index.remove(pdoc.id);
+        index.add(pdoc);
+    });
+
+    ctx.on('problem/del', async (domainId, docId) => {
+        index.remove(`${domainId}/${docId}`);
+    });
+}
diff --git a/packages/flexsearch/package.json b/packages/flexsearch/package.json
new file mode 100644
index 000000000..92ca68d6e
--- /dev/null
+++ b/packages/flexsearch/package.json
@@ -0,0 +1,7 @@
+{
+    "name": "@hydrooj/flexsearch",
+    "version": "0.0.1",
+    "dependencies": {
+        "flexsearch": "^0.7.31"
+    }
+}