agents.md is read before doing any work

How codex discovers guidance:

The instruction chain:

1.Global scope:

in your Codex directory(default~/.codex): u can also use AGENTS.override.md,but only the first non-empty AGENTS.md is read

2.Project scope:

At the project root in each directory along the path,it checks for AGENTS.override.md ,then AGENTS.md,then any fallback names in project_doc_fallback_filenames. Codex includes at most one file per directory

3.Merge order:

The later ,the higher : because they appear later in the prompt

Create global guidance:

1.make sure the directory exist: 2.create with reusable preference 3.run codex anywhere to confirm it loads the file

if you want a temporary global ,use AGENTS.override.md

Layer project instructions:

1.In your repository root, add an AGENTS.md that covers basic setup 2.Add overrides in nested directories when specific teams need different rules. For example, inside services/payments/ create AGENTS.override.md 3.Start Codex from the payments directory:

Add code reviews rules:

For Codex code review in GitHub, add a ## Code Review Rules section to the AGENTS.md closest to the code the rules govern. Put repository-wide checks at the root and service-specific checks in a nested file.

Customize fallback filenames:

if u use a customize filename,add it to the fallback list then Codex can really read it as a instructions file: 1.edit your Codex configuration

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# ~/.codex/config.toml
project_doc_fallback_filenames = ["TEAM_GUIDE.md", ".agents.md"]
project_doc_max_bytes = 65536

2.Restart Codex or run a new command to update configuration loads: