A2A Message Types — Text, Files, and Structured Data

Why it matters

Rich message content unlocks realistic agent use cases: code review with file attachments, data analysis with structured inputs. Understanding the message model shapes what your agents can do.

The architecture

Part types: text (string), file (bytes with MIME), data (structured JSON). Messages combine parts.

Extensibility: new part types can be defined per domain.

How it works end to end

File handling: inline for small files (base64), URI reference for large. Server-side agents fetch by URI.

Structured data: JSON with optional schema reference. Enables type-safe parameter passing.

Multi-modal: image, audio, video parts extend the model.