Advanced MCP Features 🐡/Elaboration

What you've learned

1. Advanced Tools

• Annotations: You learned to communicate intent and risk with readOnlyHint, destructiveHint, idempotentHint, and openWorldHint, improving UX and trust without confusing them for security controls.
• Structured Output & Output Schemas: You defined schemas to guarantee machine-parseable results (and saw how invalid shapes fail fast). This unlocks safer automation and downstream chaining.
• Pragmatic Guidelines: You adopted practical heuristics (e.g. idempotency focuses on core outcome, not incidental timestamps) so annotations remain meaningful instead of pedantic.

2. Elicitation

• Human-in-the-Loop Input Requests: You implemented server-initiated, structured follow-up questions mid-tool execution using elicitation/create.
• Outcome Handling: You handled all result paths (accept, decline, cancel) cleanly.
• Responsible Use: You learned to reserve elicitation for genuinely missing contextual data. Not as a crutch for weak initial prompts.

3. Sampling

• Borrowing the User's Model: Instead of bundling your own API integrations, you requested completions through the client. Respecting user controls, permissions, and model preferences.
• Prompt Crafting: You structured systemPrompt + message history for clarity, determinism, and safety (plus using examples and formatting expectations).
• Server-Side Logging: You surfaced debug + informational events back to clients to aid transparency and troubleshooting.
• Use Cases: Automated tag suggestions, summarization, and other “assistive” behaviors that keep users in the loop.

4. Long Running Tasks

• Progress Notifications: You emitted notifications/progress tied to a progressToken, giving users visibility into multi-step operations.
• Cancellation Flow: You honored notifications/cancelled, wiring cleanup with AbortController (and ensuring resource release / early exit paths).
• Resilient Async Patterns: You separated work orchestration from lifecycle signals for maintainability and correctness.

5. Changes (Dynamic Capabilities)

• list_changed Notifications: You notified clients when tools, prompts, or resources appeared, disappeared, or changed. Keeping UIs reactive without manual refresh.
• Resource Templates vs. Instances: You distinguished template availability (enable/disable) from the evolving set of expansions (e.g. DB rows, files) and triggered updates accordingly.
• Subscriptions: You pushed granular resources/updated messages only to interested clients, enabling efficient, real-time views.
• Adaptive Servers: You embraced dynamic capability surfaces. Mirroring real application states (auth, data presence, feature flags, external systems).

Putting It All Together

• Advertise rich, self-describing tools with trustworthy semantics.
• Produce and validate structured results ready for chaining or UI rendering.
• Ask users clarifying questions at exactly the right moment.
• Leverage the user's own model access for generation instead of hard-coding providers.
• Stream transparency via logs, progress, and cancellation.
• Stay in sync with clients as its surface area evolves in real time.

Suggested Next Steps

1. Refine Prompts: Introduce test fixtures for sampling prompts. Assert on shape + tone of generated outputs.
2. Add Safety Layers: Layer classification or content filtering around generative outputs where needed.
3. Observability: Pipe server logs to structured tracing/metrics for production use (keeping privacy in mind).
4. Capability Versioning: Start tagging major tool/prompt contract shifts to help clients adapt gracefully.
5. Extend Resources: Expose more dynamic domains (user workspaces, recent activity feeds, external APIs) with subscriptions where latency matters.

Conclusion