Ch 6: Prompts — Under the Hood

Ch 6 — Prompts Under the Hood

Wire formats, message roles, multi-content messages, argument completion, dynamic lists, and SDK patterns

Index ← High Level

Under the Hood

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Aprompts/list Wire FormatDiscovering available prompts and their arguments

list

prompts/listReturns array of
prompt descriptors

each has

badge

Descriptorname, description,
arguments[]

args

tune

Argumentsname, description,
required flag

arrow_downward prompts/get: fetching rendered messages

Bprompts/get Wire FormatRendering a prompt into a message sequence

send

prompts/getname + arguments
as params

renders

forum

MessagesArray of role +
content objects

roles

people

Rolesuser, assistant

arrow_downward Multi-content messages: text + resources + images

CMulti-Content MessagesA single message can contain text, resources, and images

text_snippet

TextContentPlain text
instructions

attach_file

ResourceContentEmbedded resource
with URI

image

ImageContentBase64 image
data

arrow_downward Argument completion for prompt parameters

DArgument CompletionServer suggests values for prompt arguments

edit

User TypesPartial value
for argument

complete

auto_awesome

completionref/prompt +
argument name

returns

list

SuggestionsMatching values
for the argument

arrow_downward Dynamic prompt lists and list_changed

EDynamic Prompt ListsServers can add or remove prompts at runtime

playlist_add

list_changedServer notifies
prompts changed

re-list

refresh

Re-fetchClient calls
prompts/list again

update

UI UpdatedSlash commands
refreshed

arrow_downward SDK patterns: defining prompts in code

FSDK PatternsDefining prompts in Python and TypeScript

code

Python SDK@mcp.prompt()
decorator pattern

javascript

TypeScript SDKserver.prompt()
method pattern