Agent ExplorerBeta

Payload Builder

The Payload Builder provides a structured UI for constructing valid A2A JSON-RPC message payloads without needing to write raw JSON.

Mock agent chat and payload builder

Accessing the Builder

  1. Open a project
  2. Go to the Test tab
  3. Use the advanced input options or the Payload Builder button in the toolbar

Building a Message

Basic Fields

  • Message ID — Auto-generated UUID (editable if needed)
  • Role — Always "user" for outgoing messages

Adding Parts

Click Add Part and choose a type:

Part TypeUse Case
TextPlain text content, the most common type
FileBinary file attachments (base64 encoded)
DataStructured JSON data payloads

Text Part

{ "kind": "text", "text": "Your message here" }

File Part

{
  "kind": "file",
  "file": {
    "name": "example.txt",
    "mimeType": "text/plain",
    "bytes": "SGVsbG8gV29ybGQ="
  }
}

Data Part

{
  "kind": "data",
  "data": { "customField": "value" }
}

Templates

Save frequently-used payloads as templates and reload them quickly:

  1. Build your payload
  2. Click Save as Template
  3. Give it a name
  4. Load it again from the Templates dropdown

Preview & Send

  1. Click Preview to see the full JSON-RPC envelope
  2. Verify the structure
  3. Click Send to execute the request

The response appears in the conversation view alongside the task state.