HumanLayer

HumanLayer is an API and developer SDK for building human-in-the-loop workflows into AI agents. It lets you require human approval before sensitive tool calls, contact humans as a tool for answers or feedback, and route messages across Slack, Email, Discord (coming), and other channels. The platform sits at the tool-calling layer, so you can bring your own LLM and orchestration framework (LangChain, CrewAI, ControlFlow, Vercel AI SDK, Mastra, etc.).

Key capabilities include approval decorators, granular routing to teams or individuals, escalations and timeouts, state management, learning/auto-approvals based on prior decisions, and webhooks for agent/response events. A CLI and React Embed are available for quick integration. Premium/Enterprise plans add channels like Microsoft Teams, SMS, RCS, longer retention, and deployment options (private VPC/on-prem) with RBAC/SSO.

Useful for teams shipping production agents that need reliability and oversight (e.g., sending emails, posting to CRMs, editing data, initiating payments). The core SDKs are open and the company publishes guidance like 12-Factor Agents for building dependable agent systems.