---

name: use-facet-crates description: Guidelines for using facet crates (facet-json, facet-toml, facet-args) instead of serde-based alternatives for consistent dogfooding

Use Facet Crates Instead of Serde Ecosystem

When writing code in this workspace, prefer facet-based crates over serde-based ones. This project is building facet as a replacement for serde, so we should dogfood our own libraries.

Crate Replacements

When to Use Which

Use facet-json for:

• New code in this workspace
• Internal tools (like benchmark-analyzer)
• Anything that doesn't need serde compatibility

serde_json is acceptable for:

• Interop with external crates that require serde
• Benchmarks comparing facet vs serde performance
• Code that specifically tests serde compatibility

Quick Example

Copy// OLD (serde)
use serde::{Serialize, Deserialize};
use serde_json;

#[derive(Serialize, Deserialize)]
struct Config {
    name: String,
}

let config: Config = serde_json::from_str(json)?;

// NEW (facet)
use facet::Facet;
use facet_json as json;

#[derive(Facet)]
struct Config {
    name: String,
}

let config: Config = json::from_str(json)?;

Checking Dependencies

When adding new dependencies or reviewing code, check Cargo.toml for serde ecosystem crates and consider if facet alternatives exist.

TODO for This Workspace

The benchmark-analyzer currently uses serde_json for JSON serialization in chart data. This should be migrated to facet-json for consistency (eating our own dogfood).

Location: tools/benchmark-analyzer/src/report.rs - uses serde_json::to_string() for chart labels/data.