# Sentinel

> Security monitoring for Stacks (Clarity) smart contracts. Describe what to watch, and we'll ping you when it happens.

Free: read contracts, a 90-day backtest and one real past alert; testnet and pre-launch. Builder $19 per live mainnet contract a month (up to 3). Team $399 a month ($299 founding). Protocol by arrangement. Checks $0.25 a run, $0.75 deep. Events are never billed. [Pricing](https://runsentinel.app/pricing)

Sentinel monitors and alerts; it never acts onchain. Teams respond with their own webhook handlers.

## Connect

- CLI (default): `@secondlayer/sentinel`, Node 22+; install it globally with your package manager or run it without installing. Then `sentinel login`. [Quickstart](https://runsentinel.app/docs/quickstart.md), [CLI](https://runsentinel.app/docs/cli.md)
- MCP server: `https://api.runsentinel.app/mcp` (hosted, browser sign-in, nothing installed), for clients with remote MCP. [MCP server](https://runsentinel.app/docs/mcp.md)
- Agent skill (optional, with either): https://runsentinel.app/.well-known/skills/sentinel/SKILL.md; install it with `npx skills add https://runsentinel.app`, copy it into your agent's skills folder, or read it.
- SDK: `@secondlayer/sentinel` in TypeScript. [SDK](https://runsentinel.app/docs/sdk.md)

## Docs

- [Introduction](https://runsentinel.app/docs/introduction.md)
- [Quickstart](https://runsentinel.app/docs/quickstart.md)
- [Authentication](https://runsentinel.app/docs/authentication.md)
- [Monitor a contract](https://runsentinel.app/docs/monitor-a-stacks-contract.md)
- [Admin changes](https://runsentinel.app/docs/alert-on-admin-changes.md)
- [Large outflows](https://runsentinel.app/docs/alert-on-large-outflows.md)
- [sBTC and PoX-5](https://runsentinel.app/docs/sbtc-and-pox-5-alerts.md)
- [Slack and webhooks](https://runsentinel.app/docs/stacks-alerts-to-slack-and-webhooks.md)
- [Watches & alerts](https://runsentinel.app/docs/watches-and-alerts.md)
- [Billing](https://runsentinel.app/docs/billing.md)
- [CLI](https://runsentinel.app/docs/cli.md)
- [MCP server](https://runsentinel.app/docs/mcp.md)
- [SDK](https://runsentinel.app/docs/sdk.md)
- [API reference](https://runsentinel.app/docs/api.md)

## Blog

- [Would Sentinel have caught the Arkadiko drain?](https://runsentinel.app/blog/would-sentinel-have-caught-the-arkadiko-drain): A governance proposal on Stacks installed a contract that could mint USDA and empty the vault pool. We replayed Sentinel over the chain's own blocks to see what it would have sent, and when.