Quick Start: MCP Elicitations

In this quick start, we'll demonstrate fast-agent's MCP Elicitation features.

Elicitations allow MCP Servers to request additional information from Users whilst they are running.

The demo comprises three MCP Servers and three fast-agent programs:

• An interactive demonstration showing different types of Forms, Fields and Validation.
• A demonstration of an Elicitation made during a Tool Call.
• An example of using a custom Elicitation handler.

This quick start gives provides you with a complete MCP Client and Server solution for developing and deploying Elicitations.

Setup fast-agent

Make sure you have the uv package manager installed, and open a terminal window. Then:

Linux/MacOSWindows

# create, and change to a new directory
mkdir fast-agent && cd fast-agent

# create and activate a python environment
uv venv
source .venv/bin/activate

# setup fast-agent
uv pip install fast-agent-mcp

# setup the elicitations demo 
fast-agent quickstart elicitations

# go the demo folder
cd elicitations

# create, and change to a new directory
md fast-agent |cd

# create and activate a python environment
uv venv
.venv\Scripts\activate

# setup fast-agent
uv pip install fast-agent-mcp

# setup the elicitations demo 
fast-agent quickstart elicitations

# go the demo folder
cd elicitations

You are now ready to start the demos.

Elicitation Requests and Forms

The Interactive Forms demo showcases all of the Elicitation data types and validations. Start the interactive form demo with:

uv run forms_demo.py

This demonstration displays 4 different elicitation forms in sequence.

Note that the forms:

• Can be navigated with the Tab or Arrow Keys (→\←)
• Have real time Validation
• Can be Cancelled with the Escape key
• Uses multiline text input for long fields
• Identify the Agent and MCP Server that produced the request.

The Cancel All option cancels the Elicitation Request, and automatically cancels future requests to avoid unwanted interruptions from badly behaving Servers.

For MCP Server developers, the form is fast and easy to navigate to facilitating iterative development.

The elicitation_forms_server.py file includes examples of all field types and validations: Numbers, Booleans, Enums and Strings.

It also supports the formats specified in the schema: Email, Uri, Date and Date/Time.

Tool Call

The Tool Call demo demonstrates an Elicitation being conducted during an MCP Tool Call. This also showcases a couple of fast-agent features:

• The passthrough model supports testing without an LLM. You can read more about Internal Models here.
• Calling a tool by sending a ***CALL_TOOL message, that enables an Agent to directly call an MCP Server Tool with specific arguments.

Run uv run tool_call.py to run the Agent and see the elicitation. You can use a real LLM with the --model switch.

Custom Handler

This example shows how to write and integrate a custom Elicitation handler. For this example, the agent uses a custom handler to generate a character for a game. To run:

uv run game_character.py

This agent uses a custom elicitation handler to generate a character for a game. The custom handler is in game_character_handler.py and is setup with the following code:

@fast.agent(
    "character-creator",
    servers=["elicitation_forms_server"],
    # Register our handler from game_character_handler.py
    elicitation_handler=game_character_elicitation_handler,
)

For MCP Server Developers, Custom Handlers can be used to help complete automated test flows. For Production use, Custom Handlers can be used to send notifications or request input via remote platforms such as web forms.

Configuration

Note that Elicitations are now enabled by default in fast-agent, and can be configured with the fastagent.config.yaml file.

You can configure the Elicitation mode to forms (the default),auto-cancel or none.

mcp:
  servers:
    # Elicitation test servers for different modes
    elicitation_forms_mode:
      command: "uv"
      args: ["run", "elicitation_test_server_advanced.py"]
      transport: "stdio"
      cwd: "."
      elicitation:
        mode: "forms"

In auto-cancel mode, fast-agent advertises the Elicitation capability, and automatically cancels Elicitation requests from the MCP Server.

When set to none, the Elicitation capability is not advertised to the MCP Server.