Rust logging

Skill longzhi/rust-coding-standards/skills/rust-logging

Use when setting up tracing, configuring log levels, writing structured logs, using spans and instrument, or handling sensitive data in Rust logs.From its SKILL.md

Install

npx -y skills add longzhi/rust-coding-standards --skill rust-logging

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SKILL.md

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Rust Logging Standards

Core Rules

Framework: tracing + tracing-subscriber
Format: pretty print in dev, JSON in production
Output: stdout
Language: all log messages in English

Log Levels

Level	Purpose	Example
`ERROR`	Requires alerting and human intervention	Database connection failed
`WARN`	Needs attention but system can self-heal	Retry succeeded after transient failure
`INFO`	Business events, visible in production	Order created/completed
`DEBUG`	Development debugging, disabled in prod	SQL queries, intermediate values
`TRACE`	Extreme detail, only for hard-to-diagnose issues	Function entry/exit

# Production
RUST_LOG=info,my_app=debug

# Development
RUST_LOG=debug,my_app=trace,sqlx=warn

Structured Logging

Use snake_case field names:

tracing::info!(
    request_id = %request_id,
    user_id = %user_id,
    order_id = %order.id,
    duration_ms = elapsed.as_millis() as u64,
    "order completed"
);

Common fields: request_id, user_id, order_id, duration_ms, error, path, method, status

Span Usage

#[tracing::instrument(
    name = "create_order",
    skip(self, cmd),
    fields(user_id = %cmd.user_id, product_id = %cmd.product_id)
)]
pub async fn create_order(&self, cmd: CreateOrderCommand) -> Result<Order, AppError> {
    // ...
}

Always skip large or non-Display arguments (self, request bodies, DB pools).
Use fields(...) to attach key context to the span.

Sensitive Data

Never log: passwords, API keys, tokens, credit card numbers, personal IDs.

// Use the secrecy crate
use secrecy::Secret;

pub struct Config {
    pub api_key: Secret<String>,  // Displays as [REDACTED] in logs
}

Error Logging

// ERROR: requires alerting
tracing::error!(error = ?err, "database connection failed");

// WARN: needs attention
tracing::warn!(error = ?err, attempt = attempt, "retry after failure");

// INFO: expected business error
tracing::info!(error = %err, "validation failed");

?err — preserves the full error chain (Debug format)
%err — logs only the Display message

Checklist

Use tracing macros, never println! or log
All log messages in English
Key business operations logged at INFO level
Errors use the correct severity level
Include request_id for distributed tracing
Sensitive data is redacted
Use structured fields instead of string concatenation