JetBrains introduces ThinkRail agent harness for spec-driven workflows

JetBrains has introduced ThinkRail, an experimental agent harness from its research department. Distinct from its previous JetBrains Air environment, ThinkRail is a focused tool that uses Git worktrees to isolate tasks. It implements spec-driven development using a 'spec graph' in Markdown format, providing agents with specific tools to evolve and maintain 'living specs' rather than just editing raw text.

The harness is built around the Pi agent and integrates the Monaco Editor component. The approach emphasizes a narrow product focus on specific agent workflows and tooling for spec management, contrasting with broader platforms that attempt to integrate all agents. ThinkRail is currently an experiment and not yet a finished product. The stance behind the tool is that focused, specialized agent tools with specific workflows like spec-driven development are more effective than broad, general-purpose agent platforms.