A deterministic verification engine for agents. Fires the edge cases your sandbox never sends — duplicate webhooks, declined cards, rate limits — then proves a fix: the same scenario fails on the old...
概览
Also on Smithery, npm and the official MCP registry. A deterministic verification engine for agents, as an MCP server for FetchSandbox. Your agent writes an integration. This checks whether it actually works — against a sandbox that behaves like the real provider, including the failures: retried webhooks, declined cards, rate limits, auth errors. When it finds a bug, it can propose a fix and then prove it: the same failure is run against your code before and after the diff. Green only if it reproduced first and stopped after. You get a receipt URL either way. The MCP server runs locally through Node.js. Clients can resolve npx differently; Cursor on Mac may need the full path from command -v npx. Discovery and reference tools are available without a key. Application planning, verification and managed local tunnelling require sign-in or an API key from . See Accounts. Get a real account key from https://fetchsandbox.com/keys. Run command -v npx and use that full path in ~/.
README
以下为原文 README 节选，完整内容请查看原文。
fetchsandbox-mcp
Also on Smithery, npm and the official MCP registry.
A deterministic verification engine for agents, as an MCP server for FetchSandbox.
Your agent writes an integration. This checks whether it actually works — against a sandbox that behaves like the real provider, including the failures: retried webhooks, declined cards, rate limits, auth errors.
When it finds a bug, it can propose a fix and then prove it: the same failure is run against your code before and after the diff. Green only if it reproduced first and stopped after. You get a receipt URL either way.
Install
The MCP server runs locally through Node.js. Clients can resolve npx differently; Cursor on Mac may need the full path from command -v npx.
{
"mcpServers": {
"fetchsandbox": {
"command": "npx",
"args": ["-y", "fetchsandbox-mcp@latest"],
"env": { "FETCHSANDBOX_API_KEY": "fsk_your_key_here" }
}
}
}
Discovery and reference tools are available without a key. Application planning, verification and managed local tunnelling require sign-in or an API key from https://fetchsandbox.com/keys. See Accounts.
| Client | File |
|---|---|
| Claude Code | .mcp.json in your project root, or claude mcp add |
| Claude Desktop | ~/Library/Application Support/Claude/claude_desktop_config.json |
| Cursor | ~/.cursor/mcp.json, or .cursor/mcp.json in the repo |
| Zed | ~/.config/zed/settings.json, under context_servers |
| Codex | ~/.codex/config.toml, as [mcp_servers.fetchsandbox] |
Cursor on Mac: tested setup
Get a real account key from https://fetchsandbox.com/keys. Run command -v npx
and use that full path in ~/.cursor/mcp.json. This example is for Homebrew
on Apple Silicon; replace the path if yours differs. On Windows, use
where.exe npx to locate your installed command.
{
"mcpServers": {
"fetchsandbox": {
"command": "/opt/homebrew/bin/npx",
"args": ["-y", "[email protected]"],
"env": { "FETCHSANDBOX_API_KEY": "fsk_your_key_here" }
}
}
}
Replace fsk_your_key_here privately with the real raw key, without a Bearer
prefix. The placeholder cannot authenticate. Check for a second FetchSandbox
entry in .cursor/mcp.json in your project. Fully quit and reopen Cursor after
安装
npx -y fetchsandbox-mcp@latest配置
{
"mcpServers": {
"fetchsandbox": {
"command": "npx",
"args": ["-y", "fetchsandbox-mcp@latest"],
"env": { "FETCHSANDBOX_API_KEY": "fsk_your_key_here" }
}
}
}