Handlebars for Vercel AI SDK is now available

We’re pleased to announce the first release of the Handlebar SDK, allowing you to monitor and control the actions of AI agents built with the Vercel AI SDK.

AI agents have a powerful capability to plan, reason, and act on our behalf to automate a number of both menial and difficult tasks. In 2025, we’ve seen agents become increasingly autonomous and dynamic, and are now tackling challenging domains like gaming, coding, customer support, and more. But this increased autonomy increases data, privacy, and compliance risks.

Crucially, guardrails are not enough: agents are powerful because they are dynamic, and so their checks and balances need to be dynamic as well. With the launch of our first SDK, Handlebar is taking a step towards dynamic agent governance.

With just a single line diff (from Vercel's agent class to a HandlebarAgent), the SDK plugs into your agents and monitors the request and responses at the tool level. You can define rules to block or allow actions based on criteria like the user invoking the agent, data in the context window, the model’s historic tool use, and more.

Now, you don’t need to rely on stochastic wizardry and pleading system prompts like “NEVER send emails more than once and always double check you’re sending it to the right person.” - with Handlebar, those policies can be enforced at runtime.

Check out the repository for examples, or install the package with npm i @handlebar/ai-sdk-v5 to get started.

It currently plugs into agents built with the Vercel AI SDK, but we’ll shortly be releasing support for other agent building frameworks. We’ve only been developing Handlebar for a couple of weeks, and this release represents a tiny fraction of what we’ll be launching in the coming months. Our immediate priorities include:

• Audit and telemetry logging of agent actions and violations
• Support for Langchain, OpenAI SDK, and more agent frameworks (Javascript and Python)
• Escalations to humans-in-the-loop
• General UX improvements to the SDK. There’s a lot of work to do there!

The SDK available now with a simple npm i @handlebar/ai-sdk-v5, is open source, runs locally, and takes a couple of minutes to configure. Try it out on your agents and let us know what you think - we welcome all feedback, good and bad.

If your company needs AI governance, book a call with us and we can talk through how Handlebar can help. Otherwise, join our discord and chat with the team directly.