Rust Best Practices

Comprehensive guide for writing high-quality, idiomatic, and highly optimized Rust code. Contains 179 rules across 14 categories, prioritized by impact to guide LLMs in code generation and refactoring.

When to Apply

Reference these guidelines when:

• Writing new Rust functions, structs, or modules

• Implementing error handling or async code

• Designing public APIs for libraries

• Reviewing code for ownership/borrowing issues

• Optimizing memory usage or reducing allocations

• Tuning performance for hot paths

• Refactoring existing Rust code

Rule Categories by Priority

Priority

Category

Impact

Prefix

Rules

1

Ownership & Borrowing

CRITICAL

own-

12

2

Error Handling

CRITICAL

err-

12

3

Memory Optimization

CRITICAL

mem-

15

4

API Design

HIGH

api-

15

5

Async/Await

HIGH

async-

15

6

Compiler Optimization

HIGH

opt-

12

7

Naming Conventions

MEDIUM

name-

16

8

Type Safety

MEDIUM

type-

10

9

Testing

MEDIUM

test-

13

10

Documentation

MEDIUM

doc-

11

11

Performance Patterns

MEDIUM

perf-

11

12

Project Structure

LOW

proj-

11

13

Clippy & Linting

LOW

lint-

11

14

Anti-patterns

REFERENCE

anti-

15

Quick Reference

1. Ownership & Borrowing (CRITICAL)

• own-borrow-over-clone - Prefer &T borrowing over .clone()

• own-slice-over-vec - Accept &[T] not &#x26;Vec<T>, &str not &String

• own-cow-conditional - Use Cow<'a, T> for conditional ownership

• own-arc-shared - Use Arc<T> for thread-safe shared ownership

• own-rc-single-thread - Use Rc<T> for single-threaded sharing

• own-refcell-interior - Use RefCell<T> for interior mutability (single-thread)

• own-mutex-interior - Use Mutex<T> for interior mutability (multi-thread)

• own-rwlock-readers - Use RwLock<T> when reads dominate writes

• own-copy-small - Derive Copy for small, trivial types

• own-clone-explicit - Make Clone explicit, avoid implicit copies

• own-move-large - Move large data instead of cloning

• own-lifetime-elision - Rely on lifetime elision when possible

2. Error Handling (CRITICAL)

• err-thiserror-lib - Use thiserror for library error types

• err-anyhow-app - Use anyhow for application error handling

• err-result-over-panic - Return Result, don't panic on expected errors

• err-context-chain - Add context with .context() or .with_context()

• err-no-unwrap-prod - Never use .unwrap() in production code

• err-expect-bugs-only - Use .expect() only for programming errors

• err-question-mark - Use ? operator for clean propagation

• err-from-impl - Use #[from] for automatic error conversion

• err-source-chain - Use #[source] to chain underlying errors

• err-lowercase-msg - Error messages: lowercase, no trailing punctuation

• err-doc-errors - Document errors with # Errors section

• err-custom-type - Create custom error types, not Box<dyn Error>

3. Memory Optimization (CRITICAL)

• mem-with-capacity - Use with_capacity() when size is known

• mem-smallvec - Use SmallVec for usually-small collections

• mem-arrayvec - Use ArrayVec for bounded-size collections

• mem-box-large-variant - Box large enum variants to reduce type size

• mem-boxed-slice - Use Box<[T]> instead of Vec<T> when fixed

• mem-thinvec - Use ThinVec for often-empty vectors

• mem-clone-from - Use clone_from() to reuse allocations

• mem-reuse-collections - Reuse collections with clear() in loops

• mem-avoid-format - Avoid format!() when string literals work

• mem-write-over-format - Use write!() instead of format!()

• mem-arena-allocator - Use arena allocators for batch allocations

• mem-zero-copy - Use zero-copy patterns with slices and Bytes

• mem-compact-string - Use CompactString for small string optimization

• mem-smaller-integers - Use smallest integer type that fits

• mem-assert-type-size - Assert hot type sizes to prevent regressions

4. API Design (HIGH)

• api-builder-pattern - Use Builder pattern for complex construction

• api-builder-must-use - Add #[must_use] to builder types

• api-newtype-safety - Use newtypes for type-safe distinctions

• api-typestate - Use typestate for compile-time state machines

• api-sealed-trait - Seal traits to prevent external implementations

• api-extension-trait - Use extension traits to add methods to foreign types

• api-parse-dont-validate - Parse into validated types at boundaries

• api-impl-into - Accept impl Into<T> for flexible string inputs

• api-impl-asref - Accept impl AsRef<T> for borrowed inputs

• api-must-use - Add #[must_use] to Result returning functions

• api-non-exhaustive - Use #[non_exhaustive] for future-proof enums/structs

• api-from-not-into - Implement From, not Into (auto-derived)

• api-default-impl - Implement Default for sensible defaults

• api-common-traits - Implement Debug, Clone, PartialEq eagerly

• api-serde-optional - Gate Serialize/Deserialize behind feature flag

5. Async/Await (HIGH)

• async-tokio-runtime - Use Tokio for production async runtime

• async-no-lock-await - Never hold Mutex/RwLock across .await

• async-spawn-blocking - Use spawn_blocking for CPU-intensive work

• async-tokio-fs - Use tokio::fs not std::fs in async code

• async-cancellation-token - Use CancellationToken for graceful shutdown

• async-join-parallel - Use tokio::join! for parallel operations

• async-try-join - Use tokio::try_join! for fallible parallel ops

• async-select-racing - Use tokio::select! for racing/timeouts

• async-bounded-channel - Use bounded channels for backpressure

• async-mpsc-queue - Use mpsc for work queues

• async-broadcast-pubsub - Use broadcast for pub/sub patterns

• async-watch-latest - Use watch for latest-value sharing

• async-oneshot-response - Use oneshot for request/response

• async-joinset-structured - Use JoinSet for dynamic task groups

• async-clone-before-await - Clone data before await, release locks

6. Compiler Optimization (HIGH)

• opt-inline-small - Use #[inline] for small hot functions

• opt-inline-always-rare - Use #[inline(always)] sparingly

• opt-inline-never-cold - Use #[inline(never)] for cold paths

• opt-cold-unlikely - Use #[cold] for error/unlikely paths

• opt-likely-hint - Use likely()/unlikely() for branch hints

• opt-lto-release - Enable LTO in release builds

• opt-codegen-units - Use codegen-units = 1 for max optimization

• opt-pgo-profile - Use PGO for production builds

• opt-target-cpu - Set target-cpu=native for local builds

• opt-bounds-check - Use iterators to avoid bounds checks

• opt-simd-portable - Use portable SIMD for data-parallel ops

• opt-cache-friendly - Design cache-friendly data layouts (SoA)

7. Naming Conventions (MEDIUM)

• name-types-camel - Use UpperCamelCase for types, traits, enums

• name-variants-camel - Use UpperCamelCase for enum variants

• name-funcs-snake - Use snake_case for functions, methods, modules

• name-consts-screaming - Use SCREAMING_SNAKE_CASE for constants/statics

• name-lifetime-short - Use short lowercase lifetimes: 'a, 'de, 'src

• name-type-param-single - Use single uppercase for type params: T, E, K, V

• name-as-free - as_ prefix: free reference conversion

• name-to-expensive - to_ prefix: expensive conversion

• name-into-ownership - into_ prefix: ownership transfer

• name-no-get-prefix - No get_ prefix for simple getters

• name-is-has-bool - Use is_, has_, can_ for boolean methods

• name-iter-convention - Use iter/iter_mut/into_iter for iterators

• name-iter-method - Name iterator methods consistently

• name-iter-type-match - Iterator type names match method

• name-acronym-word - Treat acronyms as words: Uuid not UUID

• name-crate-no-rs - Crate names: no -rs suffix

8. Type Safety (MEDIUM)

• type-newtype-ids - Wrap IDs in newtypes: UserId(u64)

• type-newtype-validated - Newtypes for validated data: Email, Url

• type-enum-states - Use enums for mutually exclusive states

• type-option-nullable - Use Option<T> for nullable values

• type-result-fallible - Use Result<T, E> for fallible operations

• type-phantom-marker - Use PhantomData<T> for type-level markers

• type-never-diverge - Use ! type for functions that never return

• type-generic-bounds - Add trait bounds only where needed

• type-no-stringly - Avoid stringly-typed APIs, use enums/newtypes

• type-repr-transparent - Use #[repr(transparent)] for FFI newtypes

9. Testing (MEDIUM)

• test-cfg-test-module - Use #[cfg(test)] mod tests { }

• test-use-super - Use use super::*; in test modules

• test-integration-dir - Put integration tests in tests/ directory

• test-descriptive-names - Use descriptive test names

• test-arrange-act-assert - Structure tests as arrange/act/assert

• test-proptest-properties - Use proptest for property-based testing

• test-mockall-mocking - Use mockall for trait mocking

• test-mock-traits - Use traits for dependencies to enable mocking

• test-fixture-raii - Use RAII pattern (Drop) for test cleanup

• test-tokio-async - Use #[tokio::test] for async tests

• test-should-panic - Use #[should_panic] for panic tests

• test-criterion-bench - Use criterion for benchmarking

• test-doctest-examples - Keep doc examples as executable tests

10. Documentation (MEDIUM)

• doc-all-public - Document all public items with ///

• doc-module-inner - Use //! for module-level documentation

• doc-examples-section - Include # Examples with runnable code

• doc-errors-section - Include # Errors for fallible functions

• doc-panics-section - Include # Panics for panicking functions

• doc-safety-section - Include # Safety for unsafe functions

• doc-question-mark - Use ? in examples, not .unwrap()

• doc-hidden-setup - Use # prefix to hide example setup code

• doc-intra-links - Use intra-doc links: [Vec]

• doc-link-types - Link related types and functions in docs

• doc-cargo-metadata - Fill Cargo.toml metadata

11. Performance Patterns (MEDIUM)

• perf-iter-over-index - Prefer iterators over manual indexing

• perf-iter-lazy - Keep iterators lazy, collect() only when needed

• perf-collect-once - Don't collect() intermediate iterators

• perf-entry-api - Use entry() API for map insert-or-update

• perf-drain-reuse - Use drain() to reuse allocations

• perf-extend-batch - Use extend() for batch insertions

• perf-chain-avoid - Avoid chain() in hot loops

• perf-collect-into - Use collect_into() for reusing containers

• perf-black-box-bench - Use black_box() in benchmarks

• perf-release-profile - Optimize release profile settings

• perf-profile-first - Profile before optimizing

12. Project Structure (LOW)

• proj-lib-main-split - Keep main.rs minimal, logic in lib.rs

• proj-mod-by-feature - Organize modules by feature, not type

• proj-flat-small - Keep small projects flat

• proj-mod-rs-dir - Use mod.rs for multi-file modules

• proj-pub-crate-internal - Use pub(crate) for internal APIs

• proj-pub-super-parent - Use pub(super) for parent-only visibility

• proj-pub-use-reexport - Use pub use for clean public API

• proj-prelude-module - Create prelude module for common imports

• proj-bin-dir - Put multiple binaries in src/bin/

• proj-workspace-large - Use workspaces for large projects

• proj-workspace-deps - Use workspace dependency inheritance

13. Clippy & Linting (LOW)

• lint-deny-correctness - #![deny(clippy::correctness)]

• lint-warn-suspicious - #![warn(clippy::suspicious)]

• lint-warn-style - #![warn(clippy::style)]

• lint-warn-complexity - #![warn(clippy::complexity)]

• lint-warn-perf - #![warn(clippy::perf)]

• lint-pedantic-selective - Enable clippy::pedantic selectively

• lint-missing-docs - #![warn(missing_docs)]

• lint-unsafe-doc - #![warn(clippy::undocumented_unsafe_blocks)]

• lint-cargo-metadata - #![warn(clippy::cargo)] for published crates

• lint-rustfmt-check - Run cargo fmt --check in CI

• lint-workspace-lints - Configure lints at workspace level

14. Anti-patterns (REFERENCE)

• anti-unwrap-abuse - Don't use .unwrap() in production code

• anti-expect-lazy - Don't use .expect() for recoverable errors

• anti-clone-excessive - Don't clone when borrowing works

• anti-lock-across-await - Don't hold locks across .await

• anti-string-for-str - Don't accept &String when &str works

• anti-vec-for-slice - Don't accept &#x26;Vec<T> when &[T] works

• anti-index-over-iter - Don't use indexing when iterators work

• anti-panic-expected - Don't panic on expected/recoverable errors

• anti-empty-catch - Don't use empty if let Err(_) = ... blocks

• anti-over-abstraction - Don't over-abstract with excessive generics

• anti-premature-optimize - Don't optimize before profiling

• anti-type-erasure - Don't use Box<dyn Trait> when impl Trait works

• anti-format-hot-path - Don't use format!() in hot paths

• anti-collect-intermediate - Don't collect() intermediate iterators

• anti-stringly-typed - Don't use strings for structured data

Recommended Cargo.toml Settings

[profile.release]

opt-level = 3

lto = "fat"

codegen-units = 1

panic = "abort"

strip = true

[profile.bench]

inherits = "release"

debug = true

strip = false

[profile.dev]

opt-level = 0

debug = true

[profile.dev.package."*"]

opt-level = 3  # Optimize dependencies in dev

How to Use

This skill provides rule identifiers for quick reference. When generating or reviewing Rust code:

• Check relevant category based on task type

• Apply rules with matching prefix

• Prioritize CRITICAL > HIGH > MEDIUM > LOW

• Read rule files in rules/ for detailed examples

Rule Application by Task

Task

Primary Categories

New function

own-, err-, name-

New struct/API

api-, type-, doc-

Async code

async-, own-

Error handling

err-, api-

Memory optimization

mem-, own-, perf-

Performance tuning

opt-, mem-, perf-

Code review

anti-, lint-

Sources

This skill synthesizes best practices from:

• Rust API Guidelines

• Rust Performance Book

• Rust Design Patterns

• Production codebases: ripgrep, tokio, serde, polars, axum, deno

• Clippy lint documentation

• Community conventions (2024-2025)