Ch 2: Architecture — Under the Hood

Ch 2 — Architecture Under the Hood

Connection lifecycle, message routing, client state machines, tool dispatch, and context aggregation internals

Index ← High Level

Under the Hood

Click play or press Space to begin...

Step- / 10

AClient Connection State MachineEvery client follows this lifecycle

power_settings_new

DisconnectedNo transport
initial state

connect

hourglass_top

InitializingHandshake in
progress

ready

check_circle

ConnectedNormal operation
requests flow

error/close

error

FailedTransport lost
or init rejected

arrow_downward Host startup: spawning clients from config

BHost Startup SequenceRead config → spawn transports → initialize each client

settings

Read ConfigParse mcp.json
server entries

for each

terminal

Spawn TransportStart process (stdio)
or open HTTP conn

then

handshake

InitializeHandshake + discover
tools/resources

arrow_downward Message routing: how the host dispatches tool calls

CMessage Routing & Tool DispatchLLM calls a tool → host finds the right client → forwards

psychology

LLMCalls tool:
search_issues

tool_call

route

Host RouterLookup: which client
owns this tool?

forward

swap_horiz

Client 1tools/call →
GitHub Server

arrow_downward Context aggregation: merging resources into LLM context

DContext AggregationHost merges tools + resources from all servers into one LLM prompt

list

Collect Toolstools/list from
every client

merge

Unified ListDeduplicate, prefix
if name collisions

inject

psychology

LLM ContextSystem prompt with
all available tools

arrow_downward Handling server-initiated requests (reverse flow)

EServer → Client RequestsSampling, elicitation, and roots — the reverse direction

dns

ServerNeeds LLM help
sends sampling req

sampling

swap_horiz

ClientReceives request,
forwards to host

route

laptop

HostCalls LLM, may ask
user, returns result

arrow_downward Error handling and reconnection strategies

FError Handling & ReconnectionWhat happens when things go wrong

error

Server CrashTransport dies
client detects

then

refresh

ReconnectHost retries with
backoff strategy

do_not_disturb

DegradeMark tools unavailable
other servers continue