Apex is a set of Agent Skills that give a coding agent a senior engineer's judgment when it designs, implements, reviews or investigates a change. The skills are plain files in the open Agent Skills format, so any agent that reads that format can use them, and there are packaged plugins for Claude Code and Codex.

I started it because every agent session opened the same way: me typing the same paragraph about how I want a review done, what a migration plan has to cover, and when to stop and ask. That paragraph grew into four skills, two read-only agents and an optional always-on engineering constitution. Code reviews on this site go through Apex's reviewer and investigator.

The four skills#

apex-design covers architecture, API, schema, migration and build-versus-buy decisions. apex-implement takes a feature, fix, refactor or migration from start to finish. apex-review reviews risk first and reports findings by severity. apex-investigate works out the cause of incidents, regressions, flaky tests and unexplained bugs before anyone touches the code. Each one only kicks in when the task needs it, so a one-line fix doesn't get a design review.

Install#

To install the published package for your client:

# Claude Code
claude plugin marketplace add zeybek/apex
claude plugin install apex@apex
 
# Codex
codex plugin marketplace add zeybek/apex
codex plugin add apex@apex

Or install just the skills with the GitHub CLI's gh skill, which is still in preview and also targets Cursor, Gemini CLI and most other agents:

gh skill install zeybek/apex --all
gh skill install zeybek/apex --all --agent claude-code --scope user

npx skills add zeybek/apex does the same through skills.sh. For anything else that reads skills, adapters/README.md lists the discovery paths and explains the copy or symlink install.