> ## Documentation Index
> Fetch the complete documentation index at: https://docs.getbindu.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Protocol reference

> Every type, enum, and message Bindu speaks. Split by topic so you don't have to scroll past 4,000 lines to find the one you need.

This section is the type-level truth. If you want to know what a `Task` looks like on the wire, what states it can be in, or what an `AgentCard` actually contains, the answer is on one of the pages below.

## What Bindu speaks

Bindu follows two open protocols and adds a handful of its own extensions.

| Protocol                                                                     | Version | What it covers                                                                                                        |
| ---------------------------------------------------------------------------- | ------- | --------------------------------------------------------------------------------------------------------------------- |
| **[A2A](https://github.com/a2aproject/A2A) (Agent-to-Agent)**                | v0.3.0  | The base layer — messages, tasks, agent cards, push notifications. Everything you need for one agent to call another. |
| **[AP2](https://github.com/google-agentic-commerce/AP2) (Agent Protocol 2)** | v0.1.0  | Payment mandates and the trust framework that lets agents transact without a human in the loop.                       |
| **Bindu extensions**                                                         | —       | Negotiation, credit accounting, trust levels. Marked `<NotPartOfA2A>` everywhere they appear.                         |

If you only read one page, read [Tasks and lifecycle](/bindu/protocol/tasks) — task state is the spine the rest of the protocol hangs off.

## Pages

<CardGroup cols={2}>
  <Card title="Types and enums" href="/bindu/protocol/types-and-enums">
    TaskState, TrustLevel, NegotiationStatus, IdentityProvider. The vocabulary.
  </Card>

  <Card title="Messages and parts" href="/bindu/protocol/messages-and-parts">
    TextPart, FilePart, DataPart, Message vs Artifact — the shapes content can take.
  </Card>

  <Card title="Tasks and lifecycle" href="/bindu/protocol/tasks">
    The Task object, its status, and how it moves between states.
  </Card>

  <Card title="Context management" href="/bindu/protocol/context">
    ContextId, history sessions, multi-turn conversations.
  </Card>

  <Card title="Agent negotiation" href="/bindu/protocol/negotiation">
    Price, latency, SLA agreed up front. Bindu-specific.
  </Card>

  <Card title="Security and authentication" href="/bindu/protocol/security">
    Auth schemes and how agents prove they're allowed.
  </Card>

  <Card title="Push notifications" href="/bindu/protocol/notifications">
    Webhook on task state change. Stop polling.
  </Card>

  <Card title="Payment and mandates" href="/bindu/protocol/payment">
    AP2 payment models and the mandate trust framework.
  </Card>

  <Card title="Credit system" href="/bindu/protocol/credit">
    Bindu's credit accounting layer next to x402.
  </Card>

  <Card title="Trust and identity" href="/bindu/protocol/trust">
    TrustLevel, IdentityProvider, DID verification.
  </Card>

  <Card title="Agent card and discovery" href="/bindu/protocol/agent-card">
    AgentCard, AgentCapabilities, AgentInterface. How clients find you.
  </Card>
</CardGroup>

<Note>
  This is a reference, not a tutorial. If you're trying to build an agent for the first time, go to [Your first agent](/bindu/get-started/your-first-agent) instead — you won't need most of this until you're three steps deeper.
</Note>