One source configures Claude Code and Codex

On 16/09/2026, I inspected the global agent configuration installed on my own workstation, file by file. It drives Claude Code and Codex from one local repository.

The report above describes what that inspection found: the build pipeline, the 4 execution layers, the skill router and the gaps between what was designed and what was running.

It is written from the machine, not from memory. Counts, paths and dates come from the files as they stood that day.

TL;DR

I recommend one source rendered to both agents as immutable releases, and any rule that must hold in a hook or a permission rather than in an instruction file.

On Claude Code against Codex, it depends: as of October 1, 2026, between Opus 4.8 and Opus 5.5 I preferred Codex, because I find its devX and UI better, but in practice I alternate. That is a personal preference, not a ranking.

What the report establishes

• One source feeds both agents. A single repository renders immutable releases identified by a SHA-256. Each release produces a CLAUDE.md for Claude Code, an AGENTS.md for Codex, the shared hooks and the skill catalog. Both agents read the same output.
• 4 layers split into suggested and enforced. Instructions and skills are suggestions the model may follow, while hooks and permissions are enforced by the harness on the actions they intercept. A rule that must hold does not belong in an instruction file.
• Skill routing is lexical. 95 skills do not fit in context. A UserPromptSubmit hook scores each prompt against a corpus of phrases with BM25 and a threshold calibrated per skill. It makes no network call, and with an identical index it returns the same result for the same prompt.
• 3 gaps went unnoticed because none raised an error. Hooks pinned to an older release than the current pointer, a legacy router still installed but no longer wired, and a duplicate guard in that legacy router which disqualifies a target named after a common word.

What the report does not say

The inspection itself does not rank Claude Code against Codex; the preference above is mine, dated, and not a result of the report.

It describes one installation at one date. The reusable skeleton it mentions is my shared Claude Code and Codex configuration, distributed as releases under ~/.config/ai-agents; it is not published. The report describes its structure, not an install path.

Who it is for

For someone who already runs Claude Code or Codex daily and has started to pile up skills, hooks and rules. The report is most useful at the moment a 2nd agent, a 2nd machine or a teammate enters the picture, when copying a folder stops being enough.

Related reading

The report shows the result, and these pieces cover the reasoning behind each layer:

• Portable agent configuration is a release system, not a shared folder: the stable map of source, build, install, runtime and audit.
• Portability becomes a Scale concern: why native primitives alone do not give portability.
• Your CLAUDE.md is too long: what belongs in the always-loaded file, and what does not.
• Why I combined three Claude Code skills and Claude selected my output style. Then ignored it: the evaluation behind a fused skill, and an Output Style that was selected but not followed.
• Claude Code security: the attack surface few teams audit: hooks and MCP servers as code running with your permissions.
• MCP servers: what they actually cost and when to use them: the difference between context used and tokens billed.
• Claude Code setup, level by level: the starting point if you have none of this yet.
• The AI instruction system is a product, not a config file: the same questions for a team of 6.