Borrowing it
Nothing to install: this file belongs to Edison-Watch/Custom-MCPs. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/Edison-Watch/Custom-MCPs/main/.agents/skills/local-sandbox/SKILL.mdgit clone --depth 1 https://github.com/Edison-Watch/Custom-MCPsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/edison-watch/custom-mcps/local-sandbox)<a href="https://agentmods.dev/skills/edison-watch/custom-mcps/local-sandbox"><img src="https://agentmods.dev/badge/skills/edison-watch/custom-mcps/local-sandbox.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00062 | $0.01191 |
| Opus 5 | $0.00031 | $0.00596 |
| Sonnet 5 | $0.00012 | $0.00238 |
| Haiku 4.5 | $0.00006 | $0.00119 |
Grade A, and why
local-sandbox scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 6d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 107 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Local sandbox: preview MCP-UI apps from fixtures
Render a committed MCP App bundle (mcp_server/apps/<name>/dist/mcp-app.html)
in a browser driven by canned data, so you can see and click the UI without a
running MCP server, Gmail account, OAuth, or a tunnel. The harness lives in
mcp_server/dev_preview/ (read its README.md for design details).
Use this when the task is "show me how the <app> app looks", "screenshot the
MCP App", "does the iframe render", or "preview it here in the cloud".
1. Build the preview
make preview_app APP=gmail_inbox # -> mcp_server/dev_preview/dist/gmail_inbox-preview.html
make preview_app APP=gmail_composer
APP is any directory under mcp_server/apps/. The output is one
self-contained HTML file (the app bundle is inlined), so it also renders when
opened standalone. dist/mcp-app.html is committed, so this works out of the
box; if you changed an app's frontend, run make build_apps first.
Tune the inline width to match a client (a narrow width triggers the app's single-column mobile layout):
make preview_app APP=gmail_inbox WIDTH=460
2. Confirm it actually rendered
make preview_smoke APP=gmail_inbox # headless Playwright; asserts fixture content painted
A pass means the app connected, received fixtures, and painted an app-specific marker (not just "connected but blank").
3. See it in the Claude Code cloud
The generated file is what you surface. Two ways, pick by what the user wants:
- Screenshot (static, guaranteed): drive the file with the preinstalled Chromium and send the PNG. Reliable and needs no CSP cooperation.
- Artifact (live, interactive): publish
dist/<app>-preview.htmlas an Artifact so the user can click around in the side panel. It is fully self-contained (no external requests), which satisfies the Artifact CSP.
Screenshot snippet (Chromium is preinstalled under /opt/pw-browsers in the
sandbox; bun run it from mcp_server/dev_preview/):
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 6d ago First seen · 107 lines · 62 tokens per session scan A 89faddc28105
local-sandbox is a skill published in the GitHub repository Edison-Watch/Custom-MCPs (0 stars, last pushed yesterday), licensed MIT. It adds 62 tokens to every session and 1,191 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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