diff --git a/.changeset/web-mermaid-workers.md b/.changeset/web-mermaid-workers.md
new file mode 100644
index 000000000..77033efdf
--- /dev/null
+++ b/.changeset/web-mermaid-workers.md
@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+Add Mermaid diagram rendering to the web chat. Fenced `mermaid` blocks in assistant responses now render as diagrams. KaTeX math and Mermaid diagram parsing also run in Web Workers to keep the UI responsive during live streaming.
diff --git a/apps/kimi-web/package.json b/apps/kimi-web/package.json
index 0c9349592..61675f5fa 100644
--- a/apps/kimi-web/package.json
+++ b/apps/kimi-web/package.json
@@ -18,6 +18,7 @@
     "@xterm/xterm": "^6.0.0",
     "katex": "^0.17.0",
     "markstream-vue": "^1.0.4",
+    "mermaid": "^11.15.0",
     "shiki": "^4.3.0",
     "stream-markdown": "^0.0.16",
     "vue": "^3.5.35",
diff --git a/apps/kimi-web/src/components/chat/Markdown.vue b/apps/kimi-web/src/components/chat/Markdown.vue
index dcafb4790..0dea41475 100644
--- a/apps/kimi-web/src/components/chat/Markdown.vue
+++ b/apps/kimi-web/src/components/chat/Markdown.vue
@@ -2,13 +2,23 @@
 <script setup lang="ts">
 import { computed, inject, nextTick, onMounted, onUnmounted, reactive, ref, watch } from 'vue';
 import { useI18n } from 'vue-i18n';
-import { MarkdownRender, enableKatex } from 'markstream-vue';
+import {
+  MarkdownRender,
+  enableKatex,
+  enableMermaid,
+  setKaTeXWorker,
+  clearKaTeXWorker,
+  setMermaidWorker,
+  clearMermaidWorker,
+} from 'markstream-vue';
 import type { MarkdownIt } from 'markstream-vue';
 import { useIsDark } from '../../composables/useIsDark';
 import type { FilePreviewRequest } from '../../types';
 import { collectFilePathAliases, findFilePathLinks } from '../../lib/filePathLinks';
 import { markdownRenderPlan } from '../../lib/markdownPerformance';
 import { copyTextToClipboard } from '../../lib/clipboard';
+import * as katexWorkerModule from 'markstream-vue/workers/katexRenderer.worker?worker&type=module';
+import * as mermaidWorkerModule from 'markstream-vue/workers/mermaidParser.worker?worker&type=module';
 // px-based CSS build (our app is px, not rem). Imported here so the styles
 // load wherever Markdown is used; scoped overrides below re-skin it to
 // Terminal Pro. Importing the same file from multiple components is a no-op
@@ -23,6 +33,35 @@ import 'markstream-vue/index.px.css';
 import 'katex/dist/katex.min.css';
 enableKatex();
 
+// Mermaid diagram rendering. enableMermaid() registers the default
+// `import('mermaid')` loader — same pattern as enableKatex(). Without a worker,
+// mermaid.parse() runs on the main thread; with a worker (set via
+// setMermaidWorker), the MermaidBlockNode can validate partial-stream code
+// off-thread so the UI stays responsive during live diagram output.
+enableMermaid();
+
+// ---------------------------------------------------------------------------
+// Off-main-thread workers for KaTeX and Mermaid
+//
+// Both katex.renderToString and mermaid.parse are CPU-heavy. markstream-vue
+// ships pre-built workers (katexRenderer.worker.js, mermaidParser.worker.js)
+// that follow the exact protocol its internal worker clients expect. We import
+// them via Vite's `?worker&type=module` so they're built as ES module chunks
+// (supporting code-splitting, which mermaid needs for per-diagram dynamic
+// imports).
+//
+// markstream-vue's MermaidBlockNode and MathBlockNode auto-detect the presence
+// of a worker: when set, heavy parsing/rendering is dispatched off-thread; when
+// absent, everything runs on the main thread.
+// ---------------------------------------------------------------------------
+
+// Tear down any previous worker (e.g. from HMR) before setting a new one.
+clearKaTeXWorker();
+clearMermaidWorker();
+
+setKaTeXWorker(new katexWorkerModule.default());
+setMermaidWorker(new mermaidWorkerModule.default());
+
 // Only `$$…$$` display math is rendered; single `$` inline math is disabled so
 // prices, env vars, and shell paths (`$5`, `$PATH`, `$HOME/bin`) stay literal
 // without any escaping or code-detection gymnastics. `math_block` (the $$ rule)
@@ -172,7 +211,7 @@ function processFileLinks(): void {
     const parent = text.parentElement;
     if (
       parent &&
-      !parent.closest('a, pre, .md-file-link') &&
+      !parent.closest('a, pre, .md-file-link, svg') &&
       text.data.trim().length > 0
     ) {
       textNodes.push(text);
@@ -231,6 +270,9 @@ function processMarkdownLinks(): void {
   const links = mdRef.value.querySelectorAll<HTMLAnchorElement>('a[href]');
   for (const link of links) {
     if (link.dataset.mdLinkHandled === 'true') continue;
+    // Skip links inside Mermaid SVGs — their hrefs are diagram semantics, not
+    // workspace file paths.
+    if (link.closest('svg')) continue;
     const href = link.getAttribute('href') ?? '';
     if (!isLocalLink(href)) continue;
     link.dataset.mdLinkHandled = 'true';
diff --git a/apps/kimi-web/src/env.d.ts b/apps/kimi-web/src/env.d.ts
index 840385dff..21bfa6af6 100644
--- a/apps/kimi-web/src/env.d.ts
+++ b/apps/kimi-web/src/env.d.ts
@@ -18,3 +18,12 @@ declare module '*.vue' {
   const component: DefineComponent<Record<string, never>, Record<string, never>, unknown>;
   export default component;
 }
+
+// Vite's `?worker&type=module` imports — not declared in `vite/client`,
+// which only covers `?worker`, `?worker&inline`, and `?worker&url` for classic
+// workers. ES module workers need this additional declaration so TypeScript
+// can resolve the import without errors.
+declare module '*?worker&type=module' {
+  const WorkerFactory: new () => Worker;
+  export default WorkerFactory;
+}
diff --git a/apps/kimi-web/vite.config.ts b/apps/kimi-web/vite.config.ts
index e9d145891..5334d30d5 100644
--- a/apps/kimi-web/vite.config.ts
+++ b/apps/kimi-web/vite.config.ts
@@ -47,4 +47,10 @@ export default defineConfig({
     emptyOutDir: true,
     target: 'es2022',
   },
+  // Workers that import modules with code-splitting (e.g. mermaid's dynamic
+  // diagram imports) need ES format — IIFE cannot split chunks. The app
+  // already targets ES2022 so all supported browsers handle module workers.
+  worker: {
+    format: 'es',
+  },
 });
diff --git a/docs/package.json b/docs/package.json
index e8f933887..31c057bd3 100644
--- a/docs/package.json
+++ b/docs/package.json
@@ -12,7 +12,7 @@
     "vitepress": "^1.5.0"
   },
   "dependencies": {
-    "mermaid": "^11.12.2",
+    "mermaid": "^11.15.0",
     "vitepress-plugin-llms": "^1.10.0",
     "vitepress-plugin-mermaid": "^2.0.17"
   }
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 858021436..1a4708ec3 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -184,6 +184,9 @@ importers:
       markstream-vue:
         specifier: ^1.0.4
         version: 1.0.4(katex@0.17.0)(mermaid@11.15.0)(stream-markdown@0.0.16(react@19.2.5)(shiki@4.3.0)(vue@3.5.35(typescript@6.0.2)))(vue-i18n@11.4.5(vue@3.5.35(typescript@6.0.2)))(vue@3.5.35(typescript@6.0.2))
+      mermaid:
+        specifier: ^11.15.0
+        version: 11.15.0
       shiki:
         specifier: ^4.3.0
         version: 4.3.0
@@ -311,7 +314,7 @@ importers:
   docs:
     dependencies:
       mermaid:
-        specifier: ^11.12.2
+        specifier: ^11.15.0
         version: 11.15.0
       vitepress-plugin-llms:
         specifier: ^1.10.0