diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 5a9dace..fd27d94 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -149,8 +149,9 @@ Claude Code assistant `tool_use` blocks carry a `name` string (e.g. `"Read"`, `"
 2. **`models/tool_results.py`** — add the name to `ToolNameLiteral` and, when the tool has a distinct result payload, add the TypedDict, type guard (`is_*_tool_result`), and union member on `ToolResultUnion`.
 3. **`utils/md_exporter.py`** — add an `elif name == "…"` branch in `_render_tool_use` (sync test parses these branches).
 4. **`static/js/render/registry.js`** — add a `TOOL_USE_RENDERERS` entry (and a `tool_use/*.js` renderer module).
-5. **Optional result UI** — if the backend emits a new `result_type`, add `TOOL_RESULT_RENDERERS` and a `tool_result/*.js` module.
-6. Run `pytest tests/test_tool_dispatch_sync.py -v` — failure names the site missing the new type.
+5. Regenerate **`static/tool_types.json`**: `python scripts/gen_tool_types_manifest.py`
+6. **Optional result UI** — if the backend emits a new `result_type`, add `TOOL_RESULT_RENDERERS` and a `tool_result/*.js` module.
+7. Run `pytest tests/test_tool_dispatch_sync.py -v` — failure names the site missing the new type.
 
 ## Getting help
 
diff --git a/Makefile b/Makefile
index d3d6d9b..bfb00cc 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-.PHONY: seed-baselines-local update-baselines check-benchmarks clean-benchmark-artifacts
+.PHONY: seed-baselines-local update-baselines gen-tool-types-manifest check-benchmarks clean-benchmark-artifacts
 
 # WARNING: captures timings on THIS machine. Production baselines must match ubuntu-latest CI.
 # Prefer downloading benchmark-results.json from a CI artifact, then:
@@ -11,6 +11,9 @@ seed-baselines-local:
 # Deprecated alias — kept for muscle memory; see seed-baselines-local warning above.
 update-baselines: seed-baselines-local
 
+gen-tool-types-manifest:
+	PYTHONPATH=. python scripts/gen_tool_types_manifest.py
+
 check-benchmarks:
 	PYTHONPATH=. pytest tests/benchmarks/ --benchmark-only --benchmark-json=benchmark-results.json -o addopts=
 	PYTHONPATH=. python scripts/check_benchmark_regression.py benchmark-results.json benchmarks/baselines.json
diff --git a/docs/architecture.md b/docs/architecture.md
index 86fdb59..b2ea3bb 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -106,6 +106,7 @@ The UI is a **hash-routed** SPA with ES modules under `static/js/`:
 - `app.js` — routing and boot
 - `projects.js`, `sessions.js`, `search.js`, `export.js` — route handlers
 - `render/registry.js` — **tool dispatch registry** for session UI: `TOOL_USE_RENDERERS` and `TOOL_RESULT_RENDERERS` map tool name / `result_type` → render function (one module per type under `render/tool_use/` and `render/tool_result/`). Parallels backend `utils/tool_dispatch.py` (backend uses ordered predicates; frontend uses direct key lookup + fallback).
+- `static/tool_types.json` — generated manifest of backend tool-use names (`python scripts/gen_tool_types_manifest.py` from `KNOWN_TOOL_TYPES`). Fetched non-blocking at boot by `render/tool_types_manifest.js` (`void initToolTypesManifest()` in `app.js`), which cross-checks `TOOL_USE_RENDERERS` and logs `console.warn` on drift.
 - `shared/markdown.js` — markdown + **DOMPurify** sanitization (do not render raw LLM HTML)
 - `shared/state.js`, `shared/utils.js`, `shared/theme.js` — shared UI state and helpers
 
diff --git a/scripts/gen_tool_types_manifest.py b/scripts/gen_tool_types_manifest.py
new file mode 100644
index 0000000..adde3ba
--- /dev/null
+++ b/scripts/gen_tool_types_manifest.py
@@ -0,0 +1,36 @@
+#!/usr/bin/env python3
+"""Write ``static/tool_types.json`` from ``KNOWN_TOOL_TYPES``.
+
+Run after adding a tool type to ``utils/tool_dispatch.py``::
+
+    python scripts/gen_tool_types_manifest.py
+"""
+
+from __future__ import annotations
+
+import json
+import sys
+from pathlib import Path
+
+_REPO_ROOT = Path(__file__).resolve().parents[1]
+_MANIFEST_PATH = _REPO_ROOT / "static" / "tool_types.json"
+
+
+def write_tool_types_manifest(path: Path | None = None) -> int:
+    if str(_REPO_ROOT) not in sys.path:
+        sys.path.insert(0, str(_REPO_ROOT))
+    from utils.tool_dispatch import KNOWN_TOOL_TYPES
+
+    dest = path or _MANIFEST_PATH
+    payload = {"tool_types": sorted(KNOWN_TOOL_TYPES)}
+    dest.write_text(json.dumps(payload, indent=2) + "\n", encoding="utf-8")
+    return len(KNOWN_TOOL_TYPES)
+
+
+def main() -> None:
+    count = write_tool_types_manifest()
+    print(f"Wrote {count} tool types to {_MANIFEST_PATH}")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/static/js/app.js b/static/js/app.js
index d472670..f362138 100644
--- a/static/js/app.js
+++ b/static/js/app.js
@@ -8,6 +8,7 @@ import { HLJS_THEME_SHEETS, applyTheme, toggleTheme } from './shared/theme.js';
 import { showProjects } from './projects.js';
 import { showWorkspace, loadSession } from './sessions.js';
 import { showSearchPage } from './search.js';
+import { initToolTypesManifest } from './render/tool_types_manifest.js';
 
 // ==================== Router ====================
 
@@ -52,6 +53,7 @@ document.addEventListener('DOMContentLoaded', () => {
     applyTheme(localStorage.getItem('theme') || 'dark');
     const yearEl = document.getElementById('footer-year');
     if (yearEl) yearEl.textContent = new Date().getFullYear();
+    void initToolTypesManifest();
     handleRoute();
     window.addEventListener('hashchange', handleRoute);
 
diff --git a/static/js/app.test.js b/static/js/app.test.js
index c2a255e..c034155 100644
--- a/static/js/app.test.js
+++ b/static/js/app.test.js
@@ -23,6 +23,9 @@ vi.mock('./shared/theme.js', () => ({
     toggleTheme,
     setWorkspaceMode: vi.fn(),
 }));
+vi.mock('./render/tool_types_manifest.js', () => ({
+    initToolTypesManifest: vi.fn().mockResolvedValue(undefined),
+}));
 
 describe('router (app.js)', () => {
     const origScrollTo = window.scrollTo;
diff --git a/static/js/render/registry.js b/static/js/render/registry.js
index 893a8dd..7179bb8 100644
--- a/static/js/render/registry.js
+++ b/static/js/render/registry.js
@@ -66,9 +66,10 @@ function getToolUseRenderer(name) {
 }
 
 function getToolResultRenderer(resultType) {
-    return Object.prototype.hasOwnProperty.call(TOOL_RESULT_RENDERERS, resultType)
-        ? TOOL_RESULT_RENDERERS[resultType]
-        : renderToolResultFallback;
+    if (Object.prototype.hasOwnProperty.call(TOOL_RESULT_RENDERERS, resultType)) {
+        return TOOL_RESULT_RENDERERS[resultType];
+    }
+    return renderToolResultFallback;
 }
 
 export function renderToolUse(tool) {
diff --git a/static/js/render/registry.test.js b/static/js/render/registry.test.js
index 432225e..28ee6b8 100644
--- a/static/js/render/registry.test.js
+++ b/static/js/render/registry.test.js
@@ -133,12 +133,13 @@ describe('getToolSummary', () => {
 });
 
 describe('renderToolUse fallback', () => {
-    it('uses JSON fallback for unknown tools', () => {
+    it('uses JSON fallback for unknown tools with raw type name', () => {
         const html = renderToolUse({
             name: 'UnknownToolXYZ',
             input: { foo: 'bar' },
         });
         expect(html).toContain('tool-call');
+        expect(html).toContain('Unknown tool: UnknownToolXYZ');
         expect(html).toContain('"foo"');
         expect(TOOL_USE_RENDERERS.UnknownToolXYZ).toBeUndefined();
     });
@@ -188,15 +189,20 @@ describe('renderTodoWriteResult', () => {
 });
 
 describe('renderToolResult fallback', () => {
-    it('renders summary-only for unknown result types', () => {
-        const html = renderToolResult({ result_type: 'custom_type' });
-        expect(html).toContain('Tool result (custom_type)');
+    it('renders raw result type and JSON payload for unknown result types', () => {
+        const html = renderToolResult({
+            result_type: 'custom_type',
+            payload: { answer: 42 },
+        });
+        expect(html).toContain('Unknown tool result: custom_type');
         expect(html).toContain('tool-result');
+        expect(html).toContain('"answer"');
+        expect(html).toContain('42');
     });
 
     it('uses fallback when result_type is an inherited property (e.g. constructor)', () => {
         const html = renderToolResult({ result_type: 'constructor' });
-        expect(html).toContain('Tool result (constructor)');
+        expect(html).toContain('Unknown tool result: constructor');
         expect(html).toContain('tool-result');
         expect(Object.prototype.hasOwnProperty.call(TOOL_RESULT_RENDERERS, 'constructor')).toBe(false);
     });
diff --git a/static/js/render/tool_result/fallback.js b/static/js/render/tool_result/fallback.js
index bef7425..edba1c3 100644
--- a/static/js/render/tool_result/fallback.js
+++ b/static/js/render/tool_result/fallback.js
@@ -1,8 +1,11 @@
+import { esc, truncate } from '../../shared/utils.js';
 import { finishToolResult } from './common.js';
 import { UNKNOWN_DISPATCH_KEY } from '../constants.js';
 
 export function renderToolResultFallback(parsed) {
     const rt = parsed.result_type || UNKNOWN_DISPATCH_KEY;
-    const summary = `Tool result (${rt})`;
-    return finishToolResult(summary, '');
+    const summary = `Unknown tool result: ${rt}`;
+    const payload = JSON.stringify(parsed, null, 2);
+    const body = `<pre><code>${esc(truncate(payload, 500))}</code></pre>`;
+    return finishToolResult(summary, body);
 }
diff --git a/static/js/render/tool_types_manifest.js b/static/js/render/tool_types_manifest.js
new file mode 100644
index 0000000..6e2b3fd
--- /dev/null
+++ b/static/js/render/tool_types_manifest.js
@@ -0,0 +1,48 @@
+import { TOOL_USE_RENDERERS } from './registry.js';
+
+const MANIFEST_URL = '/static/tool_types.json';
+const MANIFEST_FETCH_TIMEOUT_MS = 5000;
+
+/**
+ * Load backend tool-type manifest and cross-check ``TOOL_USE_RENDERERS``.
+ * Logs ``console.warn`` when the backend list and frontend registry diverge.
+ */
+export async function initToolTypesManifest() {
+    const controller = new AbortController();
+    const timeoutId = setTimeout(() => controller.abort(), MANIFEST_FETCH_TIMEOUT_MS);
+    try {
+        const res = await fetch(MANIFEST_URL, { signal: controller.signal });
+        if (!res.ok) {
+            console.warn(`[tool registry] Could not load ${MANIFEST_URL}: HTTP ${res.status}`);
+            return;
+        }
+        const data = await res.json();
+        const types = Array.isArray(data.tool_types) ? data.tool_types : [];
+        const manifest = new Set(types.filter((t) => typeof t === 'string'));
+
+        for (const name of manifest) {
+            if (!Object.prototype.hasOwnProperty.call(TOOL_USE_RENDERERS, name)) {
+                console.warn(
+                    `[tool registry] Backend tool type "${name}" has no TOOL_USE_RENDERERS entry`,
+                );
+            }
+        }
+        for (const name of Object.keys(TOOL_USE_RENDERERS)) {
+            if (!manifest.has(name)) {
+                console.warn(
+                    `[tool registry] TOOL_USE_RENDERERS entry "${name}" is missing from ${MANIFEST_URL}`,
+                );
+            }
+        }
+    } catch (err) {
+        if (err?.name === 'AbortError') {
+            console.warn(
+                `[tool registry] Could not load ${MANIFEST_URL}: timed out after ${MANIFEST_FETCH_TIMEOUT_MS}ms`,
+            );
+            return;
+        }
+        console.warn('[tool registry] Could not load tool types manifest:', err);
+    } finally {
+        clearTimeout(timeoutId);
+    }
+}
diff --git a/static/js/render/tool_types_manifest.test.js b/static/js/render/tool_types_manifest.test.js
new file mode 100644
index 0000000..a94b0d1
--- /dev/null
+++ b/static/js/render/tool_types_manifest.test.js
@@ -0,0 +1,70 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { initToolTypesManifest } from './tool_types_manifest.js';
+import { TOOL_USE_RENDERERS } from './registry.js';
+
+describe('initToolTypesManifest', () => {
+    beforeEach(() => {
+        vi.restoreAllMocks();
+    });
+
+    afterEach(() => {
+        vi.unstubAllGlobals();
+    });
+
+    it('cross-checks manifest against TOOL_USE_RENDERERS and warns on drift', async () => {
+        const warn = vi.spyOn(console, 'warn').mockImplementation(() => {});
+        const manifestTypes = [...Object.keys(TOOL_USE_RENDERERS), 'FutureToolXYZ'];
+        vi.stubGlobal(
+            'fetch',
+            vi.fn().mockResolvedValue({
+                ok: true,
+                json: async () => ({ tool_types: manifestTypes }),
+            }),
+        );
+
+        await initToolTypesManifest();
+
+        expect(warn).toHaveBeenCalledWith(
+            '[tool registry] Backend tool type "FutureToolXYZ" has no TOOL_USE_RENDERERS entry',
+        );
+    });
+
+    it('warns when fetch fails', async () => {
+        const warn = vi.spyOn(console, 'warn').mockImplementation(() => {});
+        vi.stubGlobal('fetch', vi.fn().mockRejectedValue(new Error('network')));
+
+        await initToolTypesManifest();
+
+        expect(warn).toHaveBeenCalledWith(
+            '[tool registry] Could not load tool types manifest:',
+            expect.any(Error),
+        );
+    });
+
+    it('warns when fetch times out', async () => {
+        vi.useFakeTimers();
+        try {
+            const warn = vi.spyOn(console, 'warn').mockImplementation(() => {});
+            vi.stubGlobal(
+                'fetch',
+                vi.fn((_url, init) =>
+                    new Promise((_resolve, reject) => {
+                        init?.signal?.addEventListener('abort', () => {
+                            reject(Object.assign(new Error('aborted'), { name: 'AbortError' }));
+                        });
+                    }),
+                ),
+            );
+
+            const promise = initToolTypesManifest();
+            await vi.advanceTimersByTimeAsync(5000);
+            await promise;
+
+            expect(warn).toHaveBeenCalledWith(
+                '[tool registry] Could not load /static/tool_types.json: timed out after 5000ms',
+            );
+        } finally {
+            vi.useRealTimers();
+        }
+    });
+});
diff --git a/static/js/render/tool_use/fallback.js b/static/js/render/tool_use/fallback.js
index 1c7bbfb..72c2968 100644
--- a/static/js/render/tool_use/fallback.js
+++ b/static/js/render/tool_use/fallback.js
@@ -1,12 +1,11 @@
 import { esc, truncate } from '../../shared/utils.js';
-import { getToolSummary } from './summary.js';
 import { wrapToolUse } from './common.js';
 import { UNKNOWN_DISPATCH_KEY } from '../constants.js';
 
 export function renderToolUseFallback(tool) {
     const name = tool.name || UNKNOWN_DISPATCH_KEY;
     const inp = tool.input || {};
-    const summary = getToolSummary(name, inp);
+    const summary = `Unknown tool: ${name}`;
     const s = JSON.stringify(inp, null, 2);
     const body = `<pre><code>${esc(truncate(s, 500))}</code></pre>`;
     return wrapToolUse(summary, body);
diff --git a/static/tool_types.json b/static/tool_types.json
new file mode 100644
index 0000000..b6670c1
--- /dev/null
+++ b/static/tool_types.json
@@ -0,0 +1,15 @@
+{
+  "tool_types": [
+    "AskUserQuestion",
+    "Bash",
+    "Edit",
+    "Glob",
+    "Grep",
+    "Read",
+    "Task",
+    "TodoWrite",
+    "WebFetch",
+    "WebSearch",
+    "Write"
+  ]
+}
diff --git a/tests/test_tool_dispatch_sync.py b/tests/test_tool_dispatch_sync.py
index 7063bc0..004e79e 100644
--- a/tests/test_tool_dispatch_sync.py
+++ b/tests/test_tool_dispatch_sync.py
@@ -1,6 +1,7 @@
 """Contract test: ``KNOWN_TOOL_TYPES`` must match all four dispatch sites.
 
 Sites (each compared to ``KNOWN_TOOL_TYPES`` in ``utils/tool_dispatch.py``):
+- ``static/tool_types.json`` — generated manifest
 - ``utils/md_exporter.py`` — ``_render_tool_use`` if/elif branches (parsed)
 - ``models/tool_results.py`` — ``ToolNameLiteral``
 - ``static/js/render/registry.js`` — ``TOOL_USE_RENDERERS`` keys (parsed)
@@ -8,6 +9,7 @@
 
 from __future__ import annotations
 
+import json
 import re
 from pathlib import Path
 from typing import get_args
@@ -15,11 +17,13 @@
 import pytest
 
 from models.tool_results import ToolNameLiteral
+from scripts.gen_tool_types_manifest import write_tool_types_manifest
 from utils.tool_dispatch import KNOWN_TOOL_TYPES
 
 _REPO_ROOT = Path(__file__).resolve().parents[1]
 _FRONTEND_REGISTRY = _REPO_ROOT / "static" / "js" / "render" / "registry.js"
 _MD_EXPORTER = _REPO_ROOT / "utils" / "md_exporter.py"
+_TOOL_TYPES_MANIFEST = _REPO_ROOT / "static" / "tool_types.json"
 
 
 def _format_set_diff(expected: frozenset[str], actual: frozenset[str], site: str) -> str:
@@ -81,6 +85,40 @@ def _parse_md_exporter_tool_use_handlers(path: Path) -> frozenset[str]:
     return frozenset(names)
 
 
+def _load_manifest_tool_types(path: Path) -> frozenset[str]:
+    if not path.is_file():
+        msg = f"Missing manifest: {path} (run python scripts/gen_tool_types_manifest.py)"
+        raise ValueError(msg)
+    data = json.loads(path.read_text(encoding="utf-8"))
+    raw = data.get("tool_types")
+    if not isinstance(raw, list):
+        msg = f"Invalid tool_types in {path}: expected a JSON array"
+        raise ValueError(msg)
+    for i, item in enumerate(raw):
+        if not isinstance(item, str):
+            msg = f"Invalid tool_types[{i}] in {path}: expected string, got {type(item).__name__}"
+            raise ValueError(msg)
+    return frozenset(raw)
+
+
+def test_tool_types_manifest_matches_known_tool_types() -> None:
+    site = "static/tool_types.json"
+    try:
+        actual = _load_manifest_tool_types(_TOOL_TYPES_MANIFEST)
+    except ValueError as exc:
+        pytest.fail(f"{site}: {exc}")
+    if actual != KNOWN_TOOL_TYPES:
+        pytest.fail(_format_set_diff(KNOWN_TOOL_TYPES, actual, site))
+
+
+def test_tool_types_manifest_is_committed_and_current(tmp_path: Path) -> None:
+    """Regenerating the manifest must match the committed file."""
+    expected = tmp_path / "tool_types.json"
+    write_tool_types_manifest(expected)
+    committed = _TOOL_TYPES_MANIFEST.read_text(encoding="utf-8")
+    assert expected.read_text(encoding="utf-8") == committed
+
+
 def test_md_exporter_handlers_match_known_tool_types() -> None:
     site = "utils/md_exporter.py (_render_tool_use branches)"
     try:
@@ -99,6 +137,7 @@ def test_tool_name_literal_matches_known_tool_types() -> None:
 
 
 def test_frontend_registry_matches_known_tool_types() -> None:
+    """``TOOL_USE_RENDERERS`` keys must match ``KNOWN_TOOL_TYPES``."""
     site = "static/js/render/registry.js (TOOL_USE_RENDERERS)"
     try:
         actual = _parse_frontend_tool_use_renderers(_FRONTEND_REGISTRY)