MCP Series (05): Resources and Prompts Deep Dive — Dynamic Data, Parameterized URIs, and Multi-Turn Templates

Resources vs Tools The split: Tools → actions the LLM executes (verbs) LLM decides when to call; calls may have side effects Examples: create_issue, update_status Resources → data the LLM reads (nouns) Host decides when to inject; read-only, no side effects Examples: current Sprint status, project statistics The rule: "reading a state" → Resource. "Executing an operation" → Tool. The same data can have both: get_issue as a Tool (LLM controls when to call it), jira://issue/PROJ-101 as a Resource (Host injects automatically when relevant). Pattern 1: Dynamic Resources A static Resource returns the same data every time (like a project list). A dynamic Resource returns the current state on each read — content changes as the underlying data changes. Sprint status: every read returns live data _sprint_progress_pct = 65 @server.read_resource () async def read_resource ( uri : str ) -> str : if str ( uri ) == " jira://sprint/current " : global _sprint_progress_pct _sprint_progress_pct = min ( 100 , _sprint_progress_pct + random . randint ( 0 , 3 )) return json . dumps ({ " sprint_name " : " Sprint 42 " , " progress_pct " : _sprint_progress_pct , # ← different each time " last_updated " : datetime . now ( timezone . utc ). isoformat (), # ← timestamp changes " days_remaining " : 5 , " p0_open " : count_p0_open (), # ← tracks live state }, indent = 2 ) Test output: Read 1: progress=65% last_updated=...62+00:00 Read 2: progress=67% last_updated=...04+00:00 → ✓ data changed between reads Hardcoding sprint progress in a Prompt means the LLM works from a stale snapshot. A Dynamic Resource gives it the current number on every read. Mark the Resource as dynamic in its description so the LLM knows to re-read when it needs fresh data: Resource ( uri = " jira://sprint/current " , description = ( " Live status of the active sprint: progress, issue counts. " " Read when the user asks about sprint health. " " Re-read if you need up-to-date data — content changes over time. " # ↑ explicit