OpenAI Codex Rust Best Practices

Distilled from openai/codex codex-rs/ — a 119-crate, 2,008-file Rust workspace that ships the Codex CLI coding agent. Contains 63 rules across 11 categories, each citing the exact file in codex-rs where the pattern lives, so you can write Rust the way its top contributors (Michael Bolin, jif-oai, Ahmed Ibrahim, Eric Traut, Pavel Krymets) actually ship it. Citations were refreshed against main at commit 8a94430 (2026-05-25).

When to Apply

Reference these guidelines when:

• Writing or reviewing async Rust code that spawns tokio tasks, owns cancellation tokens, or manages long-lived background workers.
• Designing error enums, Result flows, retry loops, or layer boundaries in a library or service.
• Building a CLI tool that spawns subprocesses, enforces sandboxing, or runs LLM-generated code safely.
• Architecting a Cargo workspace with more than ~5 crates, deciding what to split out, and how to manage shared dependencies.
• Adding tests to a Rust codebase where existing tests are inline mod tests { ... } blocks and scaling is becoming painful.
• Implementing a JSON-RPC or custom wire protocol with serde — especially one that must evolve without breaking clients.
• Reading API keys or other secrets into memory, or hardening a binary that handles credentials against core dumps, debugger attach, and LD_PRELOAD.
• Enforcing a network egress allowlist that must survive DNS rebinding, or loading untrusted plugins/extensions.
• Wiring OpenTelemetry traces, logs, or metrics into a service that has privacy constraints around PII.
• Building a Ratatui-based TUI that streams LLM output, handles paste bursts, or manages raw-mode terminal state.
• Any time you find yourself reaching for .unwrap(), .lock().unwrap(), anyhow::Result<()>, or #[cfg(feature = "test")] — this skill explains what codex does instead.