Crate

syn

Parser for Rust syntax — the foundation of proc-macro crates.

What it is

syn parses Rust source code from a proc_macro::TokenStream into a typed abstract syntax tree. It represents every Rust syntactic construct — structs, enums, expressions, types, attributes — and is the foundation for all custom derive and attribute macros.

Why it is commonly used

Not a direct application dependency. syn is used to build proc-macro crates like serde_derive, thiserror, and clap's derive support. Its high repo count reflects how many crates ship their own proc-macros.

1.0k

Repositories

89%

Actively maintained

931

Updated ≤ 30 days

3.8M

Total stars

877

Owners

Counted from the Cargo.toml manifests of the 1.0k indexed repositories that declare syn as a dependency — not download counts. Dependency data last verified 2026-08-13.

Browse 1049 repositories using syn in Repos →

Often used with

Crates that show up unusually often in syn projects. The most distinctive pairings rank first — crates these projects use far more than the average indexed Rust project does, not just crates that are popular everywhere. Each percentage is the share of syn projects that also use it.

quote95.9%prettyplease11.9%proc-macro290.3%convert_case10.6%heck14.7%cargo_metadata11.1%pin-project11.5%num-bigint12%paste18.3%pretty_assertions12.5%derive_more16.8%either11.8%proptest14.3%rstest10.1%hashbrown14.5%insta11.6%strum_macros13.2%pin-project-lite10.8%cfg-if14.7%num-traits21.7%tracing-opentelemetry12%opentelemetry16.5%criterion20.1%opentelemetry_sdk14.9%

Used by these organizations

Cloudflare Mozilla AWS Microsoft Google Oxide Computer Parity Technologies Deno Zed Industries Turso PingCAP SurrealDB Embark Studios The Rust Project Fuel Labs Astral Tauri Bun OpenAI Union Warp Alacritty Meilisearch Rerun FUTO Tokio Bevy Engine Bytecode Alliance Linebender Nushell Qdrant Polars Quickwit Datadog Hyperium Embassy Actix gfx-rs probe-rs PyO3 Yew Leptos Wasmer Typst Tracel AI Serde Diesel Rayon Clap RustCrypto Servo esp-rs Paradigm Matrix.org

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