Persistent Session State

This example demonstrates session-scoped state that persists across tool calls within the same MCP session.

What it shows

State set in one tool call is readable in subsequent calls
Different clients have isolated state (same keys, different values)
Reconnecting creates a new session with fresh state

Running

HTTP transport:

bash

# Terminal 1: Start the server
uv run python server.py

# Terminal 2: Run the client
uv run python client.py

STDIO transport (in-process):

bash

uv run python client_stdio.py

Example output

text

Each line below is a separate tool call

Alice connects
  session a9f6eaa3
  set user = Alice
  set secret = alice-password
  get user → Alice
  get secret → alice-password

Bob connects (different session)
  session 0c3bffc5
  get user → not found
  get secret → not found
  set user = Bob
  get user → Bob

Alice reconnects (new session)
  session e39640e3
  get user → not found