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Get Started Free →Use when the user asks about Codex Rules behavior, injected project rules, supported rule file locations, matching, or environment configuration.
| Test case | Without → With | Effect | Δ tokens | Δ turns |
|---|---|---|---|---|
| case-01 | ✗→✓ | ▲ Improved | 9% | 0% |
| case-02 | ✗→✓ | ▲ Improved | -6% | 0% |
| case-03 | ✗→✓ | ▲ Improved | -5% | 0% |
| case-07 | ✗→✓ | ▲ Improved | -16% | 0% |
| case-09 | ✗→✓ | ▲ Improved | -27% | 0% |
Codex Rules is automatic once the plugin is enabled. It injects:
SessionStart and UserPromptSubmitapply_patch by defaultDynamic PostToolUse output is injected as additional context and is deduplicated per plugin data session. Codex Rules does not rewrite tool output.
Supported project sources:
CONTEXT.md.omo/rules/**/*.md.claude/rules/**/*.md.cursor/rules/**/*.md.github/instructions/**/*.md.github/copilot-instructions.mdSupported environment knobs:
CODEX_RULES_DISABLED=1CODEX_RULES_MODE=both|static|dynamic|offCODEX_RULES_MAX_RULE_CHARS=<number>CODEX_RULES_MAX_RESULT_CHARS=<number>CODEX_RULES_ENABLED_SOURCES=CONTEXT.md,.omo/rulesThe legacy PI_RULES_* variables are accepted as fallbacks for users migrating from pi-rules.
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