1. What ABS is and its structure

ABS stands for Agent Behavior Specification. It's a spec for describing the observable behavior of an AI agent: what it says, what tools it calls, what it responds. It's the equivalent of what OpenAPI is for REST APIs: a shared format, readable by both humans and machines, that a PO, a dev, and a QA can all read and sign off on together.

ABS is YAML. Plain text. Not code. It's a way of writing:

"The user says this, the assistant does that, and I want to verify it went well."

Here's the smallest possible ABS document:

session: Customer checks order status
behaviors:
  - actor: user
    action: says
    content: "Where is my order #8291?"

  - actor: assistant
    action: calls
    target: Orders API

  - actor: assistant
    action: informs
    content: "Your order is on the way"

That's already a complete specification. Three fields per step:

The four actors you'll always use:

• user → the customer, the one talking to the bot
• assistant → the bot you're testing
• tool → an external API or database the bot queries
• human → a real person (for when the bot transfers)

Next: Write a real conversation →