Ultrathink

Ultrathink activates the Sequential Thinking MCP tool (mcp__plugin_sequential-thinking_sequential-thinking__sequentialthinking) to enable deep, structured reasoning through complex problems.

Note: Claude Code also treats the bare word "ultrathink" in a prompt as a native extended-thinking keyword that raises the model's internal thinking budget. This skill is complementary, not a replacement: it externalizes reasoning as a visible, revisable chain of sequentialthinking tool calls in the transcript, where internal thinking is not shown. Saying "ultrathink" can trigger both at once — that is expected.

Prerequisites

This skill drives the Sequential Thinking MCP tool, provided by the companion sequential-thinking plugin in this marketplace. The MCP server must be installed and enabled for the tool to exist — if it is unavailable, enable the sequential-thinking plugin first.

The exact tool id depends on how the server is installed:

• Installed via this marketplace plugin (the normal case): Claude Code namespaces it as mcp__plugin_sequential-thinking_sequential-thinking__sequentialthinking (pattern: mcp__plugin_<plugin>_<server>__<tool>).
• Configured directly as a user/project MCP server: it appears as mcp__sequential-thinking__sequentialthinking.

If unsure, use whichever …sequentialthinking tool is listed in your available tools.

Optional: to suppress the thought-box logging the server writes to stderr, set DISABLE_THOUGHT_LOGGING=true on the server — for a plugin install, add "env": {"DISABLE_THOUGHT_LOGGING": "true"} to the server entry in the plugin's .mcp.json.