Sequential Thinking MCP

Sequential Thinking is one of the reference servers in the official Model Context Protocol repository, and it is unusual in that it connects to nothing. There is no upstream API and no credentials to configure. It exposes a single tool that gives a model a scratchpad for structured reasoning, and the server's job is to hold that chain of thoughts and return it in order. Each call records one thought along with its position in the sequence, an estimate of how many steps the problem will take, and a flag for whether more thinking is needed. The estimate can be revised upward partway through, an earlier step can be marked as a revision of a previous one, and a branch can fork an alternate line of reasoning while the main chain stays intact. The result is an externalized, inspectable trace instead of reasoning that disappears inside a single response. It suits planning, debugging, and design problems where the shape of the solution is not clear at the start and the scope grows as understanding does. Teams also use it as a first MCP install, because it demonstrates the protocol end to end without an account, and its source is a short, readable example for anyone writing a server of their own.