diff --git a/app/src/lib/sidebar/panels/GraphSource.svelte b/app/src/lib/sidebar/panels/GraphSource.svelte
index fc28117..19abd48 100644
--- a/app/src/lib/sidebar/panels/GraphSource.svelte
+++ b/app/src/lib/sidebar/panels/GraphSource.svelte
@@ -1,20 +1,23 @@
 <script lang="ts">
   import type { Graph } from '$lib/types';
+  import JsonNode from './JsonNode.svelte';
 
   const { graph }: { graph?: Graph } = $props();
 
-  function convert(g: Graph): string {
-    return JSON.stringify(
-      {
-        ...g,
-        nodes: g.nodes.map((n: object) => ({ ...n, tmp: undefined, state: undefined }))
-      },
-      null,
-      2
-    );
-  }
+  const data = $derived(
+    graph
+      ? {
+          ...graph,
+          nodes: graph.nodes.map((n: object) => ({ ...n, tmp: undefined, state: undefined }))
+        }
+      : null
+  );
 </script>
 
-<pre>
-  {graph ? convert(graph) : "No graph loaded"}
-</pre>
+<div class="overflow-auto p-2">
+  {#if data}
+    <JsonNode value={data} path="graph" />
+  {:else}
+    <span class="font-mono text-xs text-neutral-500">No graph loaded</span>
+  {/if}
+</div>
diff --git a/app/src/lib/sidebar/panels/JsonNode.svelte b/app/src/lib/sidebar/panels/JsonNode.svelte
new file mode 100644
index 0000000..2868476
--- /dev/null
+++ b/app/src/lib/sidebar/panels/JsonNode.svelte
@@ -0,0 +1,136 @@
+<script module>
+  const cache = new Map<string, Record<string, boolean>>();
+
+  function getStore(root: string): Record<string, boolean> {
+    if (!cache.has(root)) {
+      try {
+        const raw = localStorage.getItem(`json_viewer:${root}`);
+        cache.set(root, raw ? JSON.parse(raw) : {});
+      } catch {
+        cache.set(root, {});
+      }
+    }
+    return cache.get(root)!;
+  }
+
+  function readOpen(path: string, fallback: boolean): boolean {
+    const root = path.split('/')[0];
+    const store = getStore(root);
+    return path in store ? store[path] : fallback;
+  }
+
+  function writeOpen(path: string, value: boolean) {
+    const root = path.split('/')[0];
+    const store = getStore(root);
+    store[path] = value;
+    try {
+      localStorage.setItem(`json_viewer:${root}`, JSON.stringify(store));
+    } catch { /* quota exceeded etc */ }
+  }
+</script>
+
+<script lang="ts">
+  import { browser } from '$app/environment';
+  import JsonNode from './JsonNode.svelte';
+
+  let {
+    value,
+    key,
+    depth = 0,
+    path = ''
+  }: { value: unknown; key?: string; depth?: number; path?: string } = $props();
+
+  const defaultOpen = $derived(depth < 4);
+  let open = $derived(browser && path ? readOpen(path, defaultOpen) : defaultOpen);
+  let flashing = $state(false);
+
+  const isArr = $derived(Array.isArray(value));
+  const isExpandable = $derived(value !== null && typeof value === 'object');
+  const open_bracket = $derived(isArr ? '[' : '{');
+  const close_bracket = $derived(isArr ? ']' : '}');
+  const items = $derived.by(() => {
+    if (Array.isArray(value)) {
+      return (value as unknown[]).map((v, i) => [String(i), v] as [string, unknown]);
+    }
+    if (value !== null && typeof value === 'object') {
+      return Object.entries(value as Record<string, unknown>).filter(
+        ([, v]) => v !== undefined
+      );
+    }
+    return [] as [string, unknown][];
+  });
+
+  function toggle(next: boolean) {
+    open = next;
+    if (browser && path) writeOpen(path, next);
+  }
+
+  let prevJson = '';
+  let flashTimeout: ReturnType<typeof setTimeout> | null = null;
+
+  $effect(() => {
+    const json = JSON.stringify(value);
+    if (prevJson && json !== prevJson) {
+      if (flashTimeout) clearTimeout(flashTimeout);
+      flashing = true;
+      flashTimeout = setTimeout(() => {
+        flashing = false;
+        flashTimeout = null;
+      }, 500);
+    }
+    prevJson = json;
+  });
+</script>
+
+<span
+  class="font-mono text-xs leading-[1.6] rounded transition-[background-color] duration-500"
+  class:bg-white={flashing}
+>
+  {#if key !== undefined}
+    <span class="text-neutral-300">{key}</span><span class="text-neutral-600">: </span>
+  {/if}
+
+  {#if isExpandable}
+    {#if items.length === 0}
+      <span class="text-neutral-500">{open_bracket}{close_bracket}</span>
+    {:else if open}
+      {#if depth > 0}
+        <button class="w-3 text-neutral-500 hover:text-neutral-200" onclick={() => toggle(false)}>
+          ▼
+        </button>
+      {/if}
+      <span class="text-neutral-500">{open_bracket}</span>
+      <div class="pl-4 border-l border-neutral-700/60">
+        {#each items as [k, v], i (k)}
+          <div>
+            <JsonNode
+              value={v}
+              key={k}
+              depth={depth + 1}
+              path={path ? `${path}/${k}` : k}
+            />{#if i < items.length - 1}<span class="text-neutral-700">,</span>{/if}
+          </div>
+        {/each}
+      </div>
+      <span class="text-neutral-500">{close_bracket}</span>
+    {:else}
+      <button
+        class="inline text-neutral-500 hover:text-neutral-200"
+        onclick={() => toggle(true)}
+      >
+        <span class="w-3 inline-block">▶</span>
+        {open_bracket}<span class="text-neutral-600 mx-1">{items.length}</span>{close_bracket}
+      </button>
+    {/if}
+  {:else if value === null}
+    <span class="text-neutral-500!">null</span>
+  {:else if typeof value === 'boolean'}
+    <span class="text-amber-400!">{value}</span>
+  {:else if typeof value === 'number'}
+    <span class="text-sky-400!">{value}</span>
+  {:else if typeof value === 'string'}
+    <span class="text-emerald-400!">"{value}"</span>
+  {:else}
+    <span class="text-neutral-400">{String(value)}</span>
+  {/if}
+</span>
diff --git a/app/src/routes/+page.svelte b/app/src/routes/+page.svelte
index 86558d8..a442add 100644
--- a/app/src/routes/+page.svelte
+++ b/app/src/routes/+page.svelte
@@ -321,7 +321,7 @@
           hidden={!appSettings.value.debug.advancedMode}
           icon="i-[tabler--code]"
         >
-          <GraphSource graph={pm.graph ?? manager?.serialize()} />
+          <GraphSource graph={manager?.serialize()} />
         </Panel>
         <Panel
           id="benchmark"