diff --git a/README.md b/README.md
index 7e3a9d3..7bec569 100644
--- a/README.md
+++ b/README.md
@@ -63,6 +63,10 @@ the same row, always labeled:
 Requirements: Linux, Python 3.9+, a `/proc` filesystem. No dependencies, no
 root, no agent installed inside your apps.
 
+Want to see it without pointing it at your machine? `python3 server.py --demo`
+serves a canned snapshot at the same URL, which is how the screenshot above was
+made.
+
 ```bash
 git clone https://forge.binaryranch.com/sastian/vitals.git
 cd vitals
diff --git a/demo/demo-snapshot.json b/demo/demo-snapshot.json
new file mode 100644
index 0000000..6c9eb76
--- /dev/null
+++ b/demo/demo-snapshot.json
@@ -0,0 +1,1460 @@
+{
+  "snapshot": {
+    "t": 0,
+    "cores": 12,
+    "host": "workstation",
+    "total_busy": 11.42,
+    "total_pct": 95,
+    "workloads": [
+      {
+        "key": "headless",
+        "name": "Headless browser automation",
+        "cpu": 6.1,
+        "pct": 50.8,
+        "rss_mb": 5024,
+        "procs": 90,
+        "age_h": 170.5,
+        "instances": 10,
+        "roles": {
+          "gpu": 4.76,
+          "renderer": 1.31,
+          "headless browser": 0.03
+        },
+        "flags": [
+          "leaked"
+        ],
+        "tabs": [
+          {
+            "id": "stagin",
+            "title": "Staging site \u2014 product page",
+            "url": "https://staging.example.com/",
+            "task_pct": 0.2,
+            "script_share": 40,
+            "heap_mb": 0.7,
+            "nodes": 4200,
+            "port": "9551",
+            "instance": "scoped_dir01",
+            "instance_age": 170.5,
+            "proc_cores": 0.49
+          },
+          {
+            "id": "stagin",
+            "title": "Staging site \u2014 product page",
+            "url": "https://staging.example.com/",
+            "task_pct": 0.2,
+            "script_share": 40,
+            "heap_mb": 0.7,
+            "nodes": 4200,
+            "port": "9552",
+            "instance": "scoped_dir02",
+            "instance_age": 170.5,
+            "proc_cores": 0.51
+          },
+          {
+            "id": "stagin",
+            "title": "Staging site \u2014 product page",
+            "url": "https://staging.example.com/",
+            "task_pct": 0.2,
+            "script_share": 40,
+            "heap_mb": 0.7,
+            "nodes": 4200,
+            "port": "9553",
+            "instance": "scoped_dir03",
+            "instance_age": 170.5,
+            "proc_cores": 0.54
+          },
+          {
+            "id": "stagin",
+            "title": "Staging site \u2014 product page",
+            "url": "https://staging.example.com/",
+            "task_pct": 0.2,
+            "script_share": 40,
+            "heap_mb": 0.7,
+            "nodes": 4200,
+            "port": "9554",
+            "instance": "scoped_dir04",
+            "instance_age": 170.5,
+            "proc_cores": 0.57
+          },
+          {
+            "id": "stagin",
+            "title": "Staging site \u2014 product page",
+            "url": "https://staging.example.com/",
+            "task_pct": 0.2,
+            "script_share": 40,
+            "heap_mb": 0.7,
+            "nodes": 4200,
+            "port": "9555",
+            "instance": "scoped_dir05",
+            "instance_age": 170.5,
+            "proc_cores": 0.6
+          },
+          {
+            "id": "stagin",
+            "title": "Staging site \u2014 product page",
+            "url": "https://staging.example.com/",
+            "task_pct": 0.2,
+            "script_share": 40,
+            "heap_mb": 0.7,
+            "nodes": 4200,
+            "port": "9556",
+            "instance": "scoped_dir06",
+            "instance_age": 170.5,
+            "proc_cores": 0.62
+          },
+          {
+            "id": "stagin",
+            "title": "Staging site \u2014 product page",
+            "url": "https://staging.example.com/",
+            "task_pct": 0.2,
+            "script_share": 40,
+            "heap_mb": 0.7,
+            "nodes": 4200,
+            "port": "9557",
+            "instance": "scoped_dir07",
+            "instance_age": 170.5,
+            "proc_cores": 0.65
+          },
+          {
+            "id": "stagin",
+            "title": "Staging site \u2014 product page",
+            "url": "https://staging.example.com/",
+            "task_pct": 0.2,
+            "script_share": 40,
+            "heap_mb": 0.7,
+            "nodes": 4200,
+            "port": "9558",
+            "instance": "scoped_dir08",
+            "instance_age": 170.5,
+            "proc_cores": 0.68
+          },
+          {
+            "id": "stagin",
+            "title": "Staging site \u2014 product page",
+            "url": "https://staging.example.com/",
+            "task_pct": 0.2,
+            "script_share": 40,
+            "heap_mb": 0.7,
+            "nodes": 4200,
+            "port": "9559",
+            "instance": "scoped_dir09",
+            "instance_age": 170.5,
+            "proc_cores": 0.71
+          },
+          {
+            "id": "stagin",
+            "title": "Staging site \u2014 product page",
+            "url": "https://staging.example.com/",
+            "task_pct": 0.2,
+            "script_share": 40,
+            "heap_mb": 0.7,
+            "nodes": 4200,
+            "port": "9560",
+            "instance": "scoped_dir10",
+            "instance_age": 170.5,
+            "proc_cores": 0.73
+          }
+        ],
+        "verdict": "pages are idle (0.02 cores of page work) \u2014 6.92 cores burned by browser internals (compositor / raster / media), not by a tab",
+        "instances_detail": [
+          {
+            "instance": "scoped_dir01",
+            "cpu": 0.49,
+            "port": "9551",
+            "tab": "Staging site",
+            "url": "https://staging.example.com/"
+          },
+          {
+            "instance": "scoped_dir02",
+            "cpu": 0.51,
+            "port": "9552",
+            "tab": "Staging site",
+            "url": "https://staging.example.com/"
+          },
+          {
+            "instance": "scoped_dir03",
+            "cpu": 0.54,
+            "port": "9553",
+            "tab": "Staging site",
+            "url": "https://staging.example.com/"
+          },
+          {
+            "instance": "scoped_dir04",
+            "cpu": 0.57,
+            "port": "9554",
+            "tab": "Staging site",
+            "url": "https://staging.example.com/"
+          },
+          {
+            "instance": "scoped_dir05",
+            "cpu": 0.6,
+            "port": "9555",
+            "tab": "Staging site",
+            "url": "https://staging.example.com/"
+          },
+          {
+            "instance": "scoped_dir06",
+            "cpu": 0.62,
+            "port": "9556",
+            "tab": "Staging site",
+            "url": "https://staging.example.com/"
+          },
+          {
+            "instance": "scoped_dir07",
+            "cpu": 0.65,
+            "port": "9557",
+            "tab": "Staging site",
+            "url": "https://staging.example.com/"
+          },
+          {
+            "instance": "scoped_dir08",
+            "cpu": 0.68,
+            "port": "9558",
+            "tab": "Staging site",
+            "url": "https://staging.example.com/"
+          },
+          {
+            "instance": "scoped_dir09",
+            "cpu": 0.71,
+            "port": "9559",
+            "tab": "Staging site",
+            "url": "https://staging.example.com/"
+          },
+          {
+            "instance": "scoped_dir10",
+            "cpu": 0.73,
+            "port": "9560",
+            "tab": "Staging site",
+            "url": "https://staging.example.com/"
+          }
+        ],
+        "has_cdp": true,
+        "series": [
+          5.86,
+          5.69,
+          6.18,
+          5.62,
+          6.07,
+          5.9,
+          5.6,
+          6.04,
+          5.59,
+          5.97,
+          5.61,
+          5.64,
+          5.96,
+          6.34,
+          5.67,
+          5.76,
+          6.15,
+          6.46,
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+          5.93,
+          6.49,
+          5.6,
+          6.38,
+          5.83,
+          5.68,
+          5.67,
+          5.85,
+          6.33,
+          5.73,
+          6.11,
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+          5.91,
+          6.07,
+          5.6,
+          5.6,
+          5.74,
+          6.2,
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+          5.85,
+          6.12,
+          5.99,
+          5.84,
+          6.32,
+          6.22,
+          5.79,
+          6.1,
+          6.06,
+          6.4,
+          6.25,
+          5.82,
+          6.49,
+          5.67,
+          5.95,
+          6.28,
+          5.69,
+          6.02,
+          5.59,
+          6.2,
+          6.28,
+          6.1
+        ]
+      },
+      {
+        "key": "app:com.brave.Browser",
+        "name": "Brave",
+        "cpu": 2.95,
+        "pct": 24.6,
+        "rss_mb": 10860,
+        "procs": 52,
+        "age_h": 0.0,
+        "instances": 0,
+        "roles": {
+          "call (WebRTC)": 2.12,
+          "gpu": 0.4,
+          "tab renderer": 0.3,
+          "main": 0.13
+        },
+        "flags": [
+          "on a call"
+        ],
+        "tabs": [
+          {
+            "id": "video",
+            "title": "Video call \u2014 3 participants",
+            "url": "https://talk.example.com/call",
+            "task_pct": 221.0,
+            "script_share": 40,
+            "heap_mb": 812,
+            "nodes": 4200,
+            "port": "9222",
+            "instance": "9222",
+            "instance_age": 0.4,
+            "proc_cores": 3.1
+          },
+          {
+            "id": "q3for",
+            "title": "Q3 forecast \u2014 Sheets",
+            "url": "https://sheets.example.com/d/1q3",
+            "task_pct": 9.4,
+            "script_share": 40,
+            "heap_mb": 268,
+            "nodes": 4200,
+            "port": "9222",
+            "instance": "9222",
+            "instance_age": 0.4,
+            "proc_cores": 3.1
+          },
+          {
+            "id": "produc",
+            "title": "Product docs \u2014 draft",
+            "url": "https://docs.example.com/draft",
+            "task_pct": 3.1,
+            "script_share": 40,
+            "heap_mb": 121,
+            "nodes": 4200,
+            "port": "9222",
+            "instance": "9222",
+            "instance_age": 5.2,
+            "proc_cores": 3.1
+          },
+          {
+            "id": "news(",
+            "title": "News (background)",
+            "url": "https://news.example.com/",
+            "task_pct": 0.8,
+            "script_share": 40,
+            "heap_mb": 96,
+            "nodes": 4200,
+            "port": "9222",
+            "instance": "9222",
+            "instance_age": 26.0,
+            "proc_cores": 3.1
+          }
+        ],
+        "verdict": "page work: 2.35 cores across 4 tabs",
+        "instances_detail": [],
+        "has_cdp": true,
+        "series": [
+          2.53,
+          2.33,
+          2.48,
+          2.45,
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+          2.55,
+          2.57,
+          2.6,
+          2.6,
+          2.71,
+          2.75,
+          2.64,
+          2.55,
+          2.72,
+          2.7,
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+          2.94,
+          2.85,
+          2.79,
+          2.84,
+          2.87,
+          2.63,
+          2.97,
+          2.93,
+          2.97,
+          2.95
+        ]
+      },
+      {
+        "key": "docker:postgres",
+        "name": "postgres \u00b7 container",
+        "cpu": 0.62,
+        "pct": 5.2,
+        "rss_mb": 412,
+        "procs": 9,
+        "age_h": 340.2,
+        "instances": 0,
+        "roles": {
+          "container": 0.62
+        },
+        "flags": [],
+        "tabs": [],
+        "verdict": "",
+        "instances_detail": [],
+        "has_cdp": false,
+        "series": [
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+          0.68,
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+      },
+      {
+        "key": "agents:research",
+        "name": "Hermes agent \u00b7 research",
+        "cpu": 0.58,
+        "pct": 4.8,
+        "rss_mb": 2210,
+        "procs": 13,
+        "age_h": 0.3,
+        "instances": 0,
+        "roles": {
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+      {
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+        "name": "Slack",
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+        "name": "Nightly backup",
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+      {
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+        "name": "Nextcloud desktop",
+        "cpu": 0.18,
+        "pct": 1.5,
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+          "process": 0.18
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+        "flags": [],
+        "tabs": [],
+        "verdict": "",
+        "instances_detail": [],
+        "has_cdp": false,
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+      },
+      {
+        "key": "kernel",
+        "name": "Kernel",
+        "cpu": 0.08,
+        "pct": 0.7,
+        "rss_mb": 0,
+        "procs": 80,
+        "age_h": 415.0,
+        "instances": 0,
+        "roles": {
+          "kernel": 0.08
+        },
+        "flags": [],
+        "tabs": [],
+        "verdict": "",
+        "instances_detail": [],
+        "has_cdp": false,
+        "series": [
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+          0.09,
+          0.09,
+          0.1,
+          0.09,
+          0.08
+        ]
+      }
+    ],
+    "flags": [
+      {
+        "key": "headless",
+        "name": "Headless browser automation",
+        "flag": "leaked",
+        "cpu": 6.1
+      },
+      {
+        "key": "app:com.brave.Browser",
+        "name": "Brave",
+        "flag": "on a call",
+        "cpu": 2.95
+      }
+    ],
+    "tabs": [
+      {
+        "id": "video",
+        "title": "Video call \u2014 3 participants",
+        "url": "https://talk.example.com/call",
+        "task_pct": 221.0,
+        "script_share": 40,
+        "heap_mb": 812,
+        "nodes": 4200,
+        "port": "9222",
+        "instance": "9222",
+        "instance_age": 0.4,
+        "proc_cores": 3.1,
+        "browser": "Brave",
+        "key": "app:com.brave.Browser"
+      },
+      {
+        "id": "q3for",
+        "title": "Q3 forecast \u2014 Sheets",
+        "url": "https://sheets.example.com/d/1q3",
+        "task_pct": 9.4,
+        "script_share": 40,
+        "heap_mb": 268,
+        "nodes": 4200,
+        "port": "9222",
+        "instance": "9222",
+        "instance_age": 0.4,
+        "proc_cores": 3.1,
+        "browser": "Brave",
+        "key": "app:com.brave.Browser"
+      },
+      {
+        "id": "produc",
+        "title": "Product docs \u2014 draft",
+        "url": "https://docs.example.com/draft",
+        "task_pct": 3.1,
+        "script_share": 40,
+        "heap_mb": 121,
+        "nodes": 4200,
+        "port": "9222",
+        "instance": "9222",
+        "instance_age": 5.2,
+        "proc_cores": 3.1,
+        "browser": "Brave",
+        "key": "app:com.brave.Browser"
+      },
+      {
+        "id": "news(",
+        "title": "News (background)",
+        "url": "https://news.example.com/",
+        "task_pct": 0.8,
+        "script_share": 40,
+        "heap_mb": 96,
+        "nodes": 4200,
+        "port": "9222",
+        "instance": "9222",
+        "instance_age": 26.0,
+        "proc_cores": 3.1,
+        "browser": "Brave",
+        "key": "app:com.brave.Browser"
+      },
+      {
+        "id": "stagin",
+        "title": "Staging site \u2014 product page",
+        "url": "https://staging.example.com/",
+        "task_pct": 0.2,
+        "script_share": 40,
+        "heap_mb": 0.7,
+        "nodes": 4200,
+        "port": "9551",
+        "instance": "scoped_dir01",
+        "instance_age": 170.5,
+        "proc_cores": 0.49,
+        "browser": "Headless browser automation",
+        "key": "headless"
+      },
+      {
+        "id": "stagin",
+        "title": "Staging site \u2014 product page",
+        "url": "https://staging.example.com/",
+        "task_pct": 0.2,
+        "script_share": 40,
+        "heap_mb": 0.7,
+        "nodes": 4200,
+        "port": "9552",
+        "instance": "scoped_dir02",
+        "instance_age": 170.5,
+        "proc_cores": 0.51,
+        "browser": "Headless browser automation",
+        "key": "headless"
+      },
+      {
+        "id": "stagin",
+        "title": "Staging site \u2014 product page",
+        "url": "https://staging.example.com/",
+        "task_pct": 0.2,
+        "script_share": 40,
+        "heap_mb": 0.7,
+        "nodes": 4200,
+        "port": "9553",
+        "instance": "scoped_dir03",
+        "instance_age": 170.5,
+        "proc_cores": 0.54,
+        "browser": "Headless browser automation",
+        "key": "headless"
+      },
+      {
+        "id": "stagin",
+        "title": "Staging site \u2014 product page",
+        "url": "https://staging.example.com/",
+        "task_pct": 0.2,
+        "script_share": 40,
+        "heap_mb": 0.7,
+        "nodes": 4200,
+        "port": "9554",
+        "instance": "scoped_dir04",
+        "instance_age": 170.5,
+        "proc_cores": 0.57,
+        "browser": "Headless browser automation",
+        "key": "headless"
+      },
+      {
+        "id": "stagin",
+        "title": "Staging site \u2014 product page",
+        "url": "https://staging.example.com/",
+        "task_pct": 0.2,
+        "script_share": 40,
+        "heap_mb": 0.7,
+        "nodes": 4200,
+        "port": "9555",
+        "instance": "scoped_dir05",
+        "instance_age": 170.5,
+        "proc_cores": 0.6,
+        "browser": "Headless browser automation",
+        "key": "headless"
+      },
+      {
+        "id": "stagin",
+        "title": "Staging site \u2014 product page",
+        "url": "https://staging.example.com/",
+        "task_pct": 0.2,
+        "script_share": 40,
+        "heap_mb": 0.7,
+        "nodes": 4200,
+        "port": "9556",
+        "instance": "scoped_dir06",
+        "instance_age": 170.5,
+        "proc_cores": 0.62,
+        "browser": "Headless browser automation",
+        "key": "headless"
+      },
+      {
+        "id": "stagin",
+        "title": "Staging site \u2014 product page",
+        "url": "https://staging.example.com/",
+        "task_pct": 0.2,
+        "script_share": 40,
+        "heap_mb": 0.7,
+        "nodes": 4200,
+        "port": "9557",
+        "instance": "scoped_dir07",
+        "instance_age": 170.5,
+        "proc_cores": 0.65,
+        "browser": "Headless browser automation",
+        "key": "headless"
+      },
+      {
+        "id": "stagin",
+        "title": "Staging site \u2014 product page",
+        "url": "https://staging.example.com/",
+        "task_pct": 0.2,
+        "script_share": 40,
+        "heap_mb": 0.7,
+        "nodes": 4200,
+        "port": "9558",
+        "instance": "scoped_dir08",
+        "instance_age": 170.5,
+        "proc_cores": 0.68,
+        "browser": "Headless browser automation",
+        "key": "headless"
+      },
+      {
+        "id": "stagin",
+        "title": "Staging site \u2014 product page",
+        "url": "https://staging.example.com/",
+        "task_pct": 0.2,
+        "script_share": 40,
+        "heap_mb": 0.7,
+        "nodes": 4200,
+        "port": "9559",
+        "instance": "scoped_dir09",
+        "instance_age": 170.5,
+        "proc_cores": 0.71,
+        "browser": "Headless browser automation",
+        "key": "headless"
+      },
+      {
+        "id": "stagin",
+        "title": "Staging site \u2014 product page",
+        "url": "https://staging.example.com/",
+        "task_pct": 0.2,
+        "script_share": 40,
+        "heap_mb": 0.7,
+        "nodes": 4200,
+        "port": "9560",
+        "instance": "scoped_dir10",
+        "instance_age": 170.5,
+        "proc_cores": 0.73,
+        "browser": "Headless browser automation",
+        "key": "headless"
+      }
+    ],
+    "browsers": [
+      {
+        "port": 9222,
+        "tabs": 4,
+        "name": "Brave",
+        "error": ""
+      }
+    ],
+    "brave_cdp": true,
+    "self_cost": 0.05,
+    "sample_ms": 118
+  },
+  "details": {
+    "headless": {
+      "key": "headless",
+      "series": [
+        5.86,
+        5.69,
+        6.18,
+        5.62,
+        6.07,
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+        5.6,
+        5.6,
+        5.74,
+        6.2,
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+        5.85,
+        6.12,
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+        6.28,
+        5.69,
+        6.02,
+        5.59,
+        6.2,
+        6.28,
+        6.1
+      ],
+      "processes": [
+        {
+          "pid": 41210,
+          "role": "gpu",
+          "rss_mb": 82,
+          "cpu": 0.71,
+          "age_h": 170.5,
+          "cmd": "/usr/lib/chromium/chromium --type=gpu-process --use-gl=disabled",
+          "cgroup": "/user.slice/user-1000.slice/user@1000.service/app.slice/run-41210.scope",
+          "windows": [],
+          "ports": [],
+          "extra": {
+            "instance": "scoped_dir01",
+            "port": "9551"
+          },
+          "threads": [
+            {
+              "tid": "41211",
+              "name": "VizCompositorTh",
+              "ticks": 528599
+            }
+          ],
+          "why": "headless, reparented to PID 1"
+        },
+        {
+          "pid": 41208,
+          "role": "headless browser",
+          "rss_mb": 99,
+          "cpu": 0.0,
+          "age_h": 170.5,
+          "cmd": "/usr/lib/chromium/chromium --headless=new --remote-debugging-port=9551",
+          "cgroup": "",
+          "windows": [],
+          "ports": [
+            9551
+          ],
+          "extra": {
+            "port": "9551"
+          },
+          "threads": [
+            {
+              "tid": "41209",
+              "name": "brave",
+              "ticks": 402
+            }
+          ]
+        }
+      ]
+    },
+    "app:com.brave.Browser": {
+      "key": "app:com.brave.Browser",
+      "series": [
+        2.53,
+        2.33,
+        2.48,
+        2.45,
+        2.45,
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+        2.54,
+        2.73,
+        2.44,
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+        2.63,
+        2.77,
+        2.75,
+        2.78,
+        2.56,
+        2.62,
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+        2.81,
+        2.85,
+        2.55,
+        2.57,
+        2.6,
+        2.6,
+        2.71,
+        2.75,
+        2.64,
+        2.55,
+        2.72,
+        2.7,
+        2.78,
+        2.94,
+        2.85,
+        2.79,
+        2.84,
+        2.87,
+        2.63,
+        2.97,
+        2.93,
+        2.97,
+        2.95
+      ],
+      "processes": [
+        {
+          "pid": 228353,
+          "role": "call (WebRTC)",
+          "rss_mb": 811,
+          "cpu": 2.21,
+          "age_h": 168.7,
+          "cmd": "/app/brave/brave --type=renderer",
+          "cgroup": "app.slice/app-flatpak-com.brave.Browser-1.scope",
+          "windows": [
+            "Video call \u2014 3 participants"
+          ],
+          "ports": [],
+          "extra": {},
+          "threads": [
+            {
+              "tid": "2240151",
+              "name": "WebRTC_W_and_N",
+              "ticks": 442288
+            },
+            {
+              "tid": "233305",
+              "name": "ThreadPoolForeg",
+              "ticks": 122985
+            }
+          ]
+        },
+        {
+          "pid": 3213897,
+          "role": "gpu",
+          "rss_mb": 331,
+          "cpu": 0.42,
+          "age_h": 180.2,
+          "cmd": "/app/brave/brave --type=gpu-process",
+          "cgroup": "",
+          "windows": [],
+          "ports": [],
+          "extra": {},
+          "threads": [
+            {
+              "tid": "3213898",
+              "name": "VizCompositorTh",
+              "ticks": 22360
+            }
+          ]
+        }
+      ]
+    }
+  }
+}
\ No newline at end of file
diff --git a/docs/screenshot.png b/docs/screenshot.png
index c48d243..51f41a2 100644
Binary files a/docs/screenshot.png and b/docs/screenshot.png differ
diff --git a/server.py b/server.py
index 31613ec..7d30a29 100644
--- a/server.py
+++ b/server.py
@@ -602,6 +602,16 @@ class Sampler(threading.Thread):
 SAMPLER = Sampler()
 
 
+DEMO = {"data": None}
+
+
+def load_demo():
+    path = os.path.join(HERE, "demo", "demo-snapshot.json")
+    with open(path) as f:
+        DEMO["data"] = json.load(f)
+    return DEMO["data"]
+
+
 class Handler(BaseHTTPRequestHandler):
     protocol_version = "HTTP/1.1"
 
@@ -626,12 +636,20 @@ class Handler(BaseHTTPRequestHandler):
             except OSError:
                 return self._send("index.html missing", "text/plain", 500)
         if u.path == "/api/snapshot":
+            if DEMO["data"]:
+                snap = dict(DEMO["data"]["snapshot"])
+                snap["t"] = time.time()
+                snap["demo"] = True
+                return self._send(json.dumps(snap))
             with SAMPLER.lock:
                 return self._send(json.dumps(SAMPLER.latest))
         if u.path == "/api/detail":
             key = parse_qs(u.query).get("key", [""])[0]
             if not key:
                 return self._send('{"error":"key required"}', code=400)
+            if DEMO["data"]:
+                return self._send(json.dumps(
+                    DEMO["data"]["details"].get(key, {"key": key, "processes": [], "series": []})))
             return self._send(json.dumps(SAMPLER.detail(key)))
         return self._send("not found", "text/plain", 404)
 
@@ -640,8 +658,14 @@ def main():
     ap = argparse.ArgumentParser()
     ap.add_argument("--port", type=int, default=int(os.environ.get("VITALS_PORT", 8791)))
     ap.add_argument("--host", default="127.0.0.1")
+    ap.add_argument("--demo", action="store_true",
+                    help="serve the canned demo snapshot (documentation, screenshots, UI work)")
     args = ap.parse_args()
-    SAMPLER.start()
+    if args.demo:
+        load_demo()
+        print("Vitals in DEMO mode — canned data, no /proc sampling, no CDP", flush=True)
+    else:
+        SAMPLER.start()
     time.sleep(1.2)
     try:
         srv = ThreadingHTTPServer((args.host, args.port), Handler)