SnapStack

How it works

SnapStack has two halves: this extension and a small always-on
local server that holds the stack and serves it to
your LLM. Both install in a couple of minutes — see Installation.

[extension] click → capture ┐
                            ▼
                      [local server]
                            ├─ stores →  a folder on your disk
                            └─ MCP    ←  your LLM client asks for the screenshots

1. You browse and capture the screens you care about — they pile up in a local stack.
2. Your LLM client calls SnapStack's MCP tools and gets a list of the pending shots.
3. It reads the ones it needs, straight from your disk. The captures stay until you clear them.

The capture dropdown follows your browser's language, falling back to English.
Supported languages: English, French, Spanish, German, Italian, Japanese, Portuguese-BR, Russian,
Simplified Chinese.

Installation

1. Install the local server

The server ships on npm and installation is straightforward on macOS, Linux and Windows:

• Install globally: npm i -g snapstack-server
• Enable background service: snapstack enable

SnapStack auto-starts on login, restarts on crash, and updates itself on each launch.
To check its status or if an update is available, simply run snapstack in your
terminal.

2. Register SnapStack with your MCP client

The server speaks MCP over HTTP at http://127.0.0.1:4123/mcp.

• Claude Code: claude mcp add --transport http --scope user snapstack http://127.0.0.1:4123/mcp
• Other clients — add an HTTP MCP server; most accept this shape (consult your client's docs for the exact syntax):

{
    "mcpServers": {
        "snapstack": { "type": "http", "url": "http://127.0.0.1:4123/mcp" }
    }
}

Clients that only spawn a process (stdio transport) — point them at the
snapstack mcp command:

{
    "mcpServers": {
        "snapstack": { "command": "npx", "args": ["-y", "-p", "snapstack-server", "snapstack", "mcp"] }
    }
}

3. Install the extension

Browser	Install
Chrome	Chrome Web Store
Edge	Chrome Web Store (Edge supports Chrome Web Store extensions)
Firefox	Firefox Add-ons

Exposed MCP tools

Your LLM client uses these three tools — no image bytes are ever pushed to the model.
It gets a lightweight list and reads only the files it wants.

Tool	Read-only	What it does
count_screenshots	Yes	Just how many captures are waiting.
get_screenshots	Yes	Lists the pending captures (number, file path, size, page URL/title). Pass numbers (e.g. [1,3]) for specific ones, otherwise all of them.
clear_screenshots	No	Removes captures from the stack: it's the only destructive tool. Pass numbers (e.g. [1,3]) for specific ones, otherwise all of them.

Use it with Claude

Two touches make SnapStack feel native in Claude Code.

Skip the per-call confirmation

Add to ~/.claude/settings.json:

{
  "permissions": {
    "allow": [
      "mcp__snapstack__count_screenshots",
      "mcp__snapstack__get_screenshots",
      "mcp__snapstack__clear_screenshots"
    ]
  }
}

Add a snap shortcut

Drop this in your ~/.claude/CLAUDE.md so a single word pulls in your captures.
Now you just capture in the browser and type snap — Claude reads exactly what's on your screen.

## Snap

When the user types **`snap`** (alone, with an instruction, and/or with capture numbers): drive the **`snapstack` MCP
server** (`mcp__snapstack__*`) — retrieve/clear pending browser screenshots, then act in context.
`get_screenshots` returns a **read-only** JSON manifest (`number`, absolute `path`, `width`/`height`, `url`, `title`,
`capturedAt`, `format`, `bytes`) — no image bytes, never deletes; read a `path` only when you need the pixels.
`clear_screenshots` is the **only** deletion, always on demand.
Numbers are the two-digit badges; pass them as **integers** (`01 02 05` → `[1, 2, 5]`).

| Input                             | Action                                                        |
|-----------------------------------|---------------------------------------------------------------|
| `snap <instruction>`              | `get_screenshots` (all) → process **all** per the instruction |
| `snap 01 02 05 <instruction>`     | `get_screenshots {numbers:[1,2,5]}` → process **those**       |
| `snap clear` / `snap clear 01 02` | `clear_screenshots` (all / those)                             |
| `snap` (bare)                     | `get_screenshots` (all) → use per context                     |

**If MCP is unavailable, tools are deferred:** try `ToolSearch` (`select:mcp__snapstack__get_screenshots`); if still
missing, tell the user and fall back to the manual path (paste image / give a file path). Never block on `snap`.

Troubleshooting

• "Capture server not started" message: the local server isn't running. Start it (or check
  its auto-start); see snapstack-server.
• Red exclamation badge: the extension can't reach the server. Make sure it's running on
  127.0.0.1:4123.
• Captures saved as PNG: your browser can't encode WebP, so SnapStack falls back to PNG
  automatically.

Support

• A question or an idea? → GitHub Discussions
• Found a bug? → open an issue

Privacy & License

MIT, no data collection, nothing leaves your computer.
See PRIVACY.md
& LICENSE.