wtf is nucleus-marketplace?

Nucleus is a plugin for AI coding agents such as Claude Code and Codex. Rather than helping the AI write more code, it adds discipline around how that code gets produced, so every step the AI takes leaves behind output that can be checked for structure, kept within defined boundaries, and traced back to a decision. The README explains the problem it targets: it is not that AI writes wrong code, but that once it finishes, nobody can easily tell what it actually did, what it based its decisions on, or whether the result should be trusted. Common issues it names include starting to code before requirements are clear, losing track of which version of a change was actually confirmed by a human, an AI reviewing its own work in the same chain that produced it, and decisions that only exist in a chat history that eventually gets summarized away and lost. To address this, each unit of work Nucleus manages, called a Skill, has a defined input and output format described as a JSON schema. Rules about which files and folders can be written to are checked automatically while the agent runs, and a violation blocks the action rather than being silently allowed. Before any request for human review goes out, an independent sub agent runs a pre-review check first. If something fails, the tool's stated policy is to alert and block rather than quietly downgrading or skipping the check. Nucleus provides 26 separate Skills covering the development lifecycle, from analyzing a requirement and building a plan, through implementing a feature with multiple review passes, to generating and running tests, and finally assembling delivery evidence such as a pull request draft. It requires an AGENTS.md file at the root of the target code repository, which it treats as the primary source of truth, and the target repository must already be a git repository. It installs into Claude Code or Codex through a plugin marketplace command, and is intended for teams that already have a code review process and want AI generated work to plug into it with a clear trail of evidence.