Agent Capabilities

Capabilities enable discovery and interoperability between agents, clients, and models. WebAgents uses the UAMP unified capabilities format.

Unified Format

All capability declarations (model, client, agent) use the same structure:

from webagents.uamp import Capabilities

# Model capabilities
model_caps = Capabilities(
    id="gpt-4o",
    provider="openai",
    modalities=["text", "image"],
    supports_streaming=True,
    context_window=128000
)

# Client capabilities  
client_caps = Capabilities(
    id="web-app",
    provider="robutler",
    modalities=["text", "image", "audio"],
    widgets=["chart", "form"],
    extensions={"supports_html": True}
)

# Agent capabilities
agent_caps = Capabilities(
    id="my-agent",
    provider="webagents",
    modalities=["text", "image"],
    provides=["web_search", "chart", "tts"],
    endpoints=["/api/search"]
)

The `provides` Parameter

Decorators support a provides parameter to declare what capability they provide:

Tools

from webagents import tool

@tool(provides="web_search")
async def search_web(query: str) -> str:
    """Search the web for information."""
    ...

@tool(provides="chart")
async def render_chart(data: str) -> str:
    """Render data as a chart widget."""
    ...

@tool(provides="tts")
async def text_to_speech(text: str) -> bytes:
    """Convert text to speech audio."""
    ...

Handoffs

from webagents import handoff

@handoff(name="gpt4", provides="thinking")
async def gpt4_handoff(messages, **kwargs):
    """GPT-4 with extended thinking."""
    ...

@handoff(name="vision", provides="image_analysis")
async def vision_handoff(messages, **kwargs):
    """Vision model for image analysis."""
    ...

HTTP Endpoints

from webagents import http

@http("/export/pdf", method="post", provides="pdf_export")
def export_pdf(data: dict) -> bytes:
    """Export data as PDF."""
    ...

@http("/api/search", provides="search_api")
def search_api(query: str) -> dict:
    """Search API endpoint."""
    ...

WebSockets

from webagents import websocket

@websocket("/stream", provides="realtime")
async def realtime_stream(ws):
    """Real-time streaming endpoint."""
    ...

Widgets

from webagents import widget

@widget(provides="chart")
def chart_widget(data: str) -> str:
    """Interactive chart widget."""
    ...

Capability Aggregation

The agent automatically aggregates all provides values from:

Tools (@tool)

Handoffs (@handoff)

HTTP endpoints (@http)

WebSockets (@websocket)

Widgets (@widget)

These are exposed via the Capabilities.provides field.

Querying Capabilities

Agents expose capabilities through the /capabilities endpoint:

curl http://localhost:8000/my-agent/capabilities

Response:

{
  "id": "my-agent",
  "provider": "webagents",
  "modalities": ["text", "image"],
  "provides": ["web_search", "chart", "tts", "pdf_export"],
  "endpoints": ["/api/search", "/export/pdf"],
  "widgets": ["chart"],
  "supports_streaming": true
}

Client Capabilities

Clients can announce their capabilities when creating a session:

from webagents.uamp import SessionCreateEvent, Capabilities

event = SessionCreateEvent(
    client_capabilities=Capabilities(
        id="web-app",
        provider="robutler",
        modalities=["text", "image", "audio"],
        widgets=["chart", "form"],
        extensions={"supports_html": True}
    )
)

This enables agents to adapt their responses based on client capabilities.

UAMP Types

Import capability types from webagents.uamp:

from webagents.uamp import (
    Capabilities,           # Unified capabilities (model, client, agent)
    ImageCapabilities,      # Detailed image support
    AudioCapabilities,      # Detailed audio support
    FileCapabilities,       # Detailed file support
    ToolCapabilities,       # Tool calling support
)

Best Practices

Use descriptive provides values - Make capabilities discoverable

Match client capabilities - Adapt output to what client can render

Aggregate from skills - Let skills declare their capabilities

Query before calling - Check agent capabilities before making requests

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