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After giving advice, a draft or a data analysis, adds 2-3 targeted follow-up questions that prompt the user to check key facts, test the reasoning and fill in missing context. Fires at most once per conversation. Official Anthropic skill.

Provides a sequential_thinking tool that guides the model to break complex problems into revisable, branching steps. Good for planning, analysis and tasks that need careful iteration. Official MCP reference server.

Official Anthropic plugin that solves competition math such as IMO and Putnam problems, with adversarial checks by an independent verifier that only sees the clean proof. Gives up explicitly rather than bluffing when unsure, and outputs LaTeX/PDF once verified.

Perplexity's official MCP with four tools: web search, grounded Q&A, deep research and reasoning, available remotely or run locally. Requires a Perplexity API key.

Anthropic's official research skill built on Fischbach and Walsh's problem-selection framework (Cell): a conversational guide to refining project ideas, assessing risk and success criteria, unblocking stalled research and choosing directions. No setup or account needed.