Ch 5: Resources & Resource Templates

Ch 5 — Resources Under the Hood

Wire formats, content types, embedded resources, SDK patterns, and list-changed notifications

Index ← High Level

Under the Hood

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AWire FormatJSON-RPC messages for resources/list and resources/read

list

resources/listRequest returns
array of descriptors

pick URI

download

resources/readRequest with URI
returns contents[]

arrow_downward Content types: text vs blob

BContent TypesText content, binary blobs, and multi-part responses

text_snippet

TextContent"text" field
UTF-8 string

image

BlobContent"blob" field
base64-encoded

multi

layers

Multi-Partcontents[] can
have many items

arrow_downward Resource templates: wire format and completion

CTemplate Wire FormatListing templates and completing parameters

view_list

templates/listReturns array of
uriTemplate objects

fill

auto_awesome

completionAutocomplete
template params

resolve

link

Read Resolvedresources/read
with concrete URI

arrow_downward Embedded resources in tool results

DEmbedded ResourcesTools can return resource references inside their results

build

Tool Calltools/call returns
a result

contains

attach_file

EmbeddedResourceResource content
inside tool result

injected

psychology

LLM ContextHost adds to
conversation

arrow_downward Subscription internals and list-changed

ESubscription InternalsSubscribe, unsubscribe, updated, and list_changed notifications

notifications

subscribeWatch a single
resource URI

notify

update

updatedContent changed
notification

playlist_add

list_changedSet of resources
added or removed

arrow_downward SDK patterns: defining resources in code

FSDK PatternsDefining resources and templates in Python and TypeScript

code

Python SDK@mcp.resource()
decorator pattern

javascript

TypeScript SDKserver.resource()
method pattern