logging-config

Development

MANDATORY - All logging code must use slog with structured fields. Load before writing any logging.

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Source SKILL.md: https://github.com/majiayu000/claude-skill-registry/blob/HEAD/skills/development/logging-config/SKILL.md

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Structured Logging Standards

Requirements

Use log/slog exclusively
Never use log.Printf(), fmt.Print(), or visual formatting (===, empty lines)
Use structured fields, not string interpolation
Single format: JSON to stdout

// Wrong
logger.Printf("WARNING: Failed to fetch %s", url)

// Right
slog.Warn("upstream fetch failed", "upstream", url, "error", err)

Setup

cooked uses a single JSON handler writing to stdout:

logger := slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
    Level: slog.LevelInfo,
}))
slog.SetDefault(logger)

No log streams, no OTel/ECS formats, no object storage — just structured JSON to stdout.

Request Log Example

Every request is logged with structured fields:

{
  "time": "2026-02-06T12:00:00Z",
  "level": "INFO",
  "msg": "request",
  "method": "GET",
  "path": "/https://cgit.internal/repo/plain/README.md",
  "upstream": "https://cgit.internal/repo/plain/README.md",
  "status": 200,
  "cache": "hit",
  "upstream_ms": 0,
  "render_ms": 12,
  "total_ms": 14,
  "content_type": "markdown",
  "bytes": 14832
}

Cache field values: hit, miss, revalidated, expired.

Log Message Style Guide

Rule	Guideline	Example
Tense	Past for events, present for conditions	`upstream fetched`, `cache full`
Case	lowercase start (no capital unless proper noun)	`config loaded`, `mermaid block found`
Punctuation	No trailing period (fragments, not sentences)	`request completed` not `Request completed.`
Redundancy	No severity prefix (level conveys this)	`upstream unreachable` not `Error: upstream unreachable`
Specificity	State what failed, not generic failure	`upstream fetch failed` not `operation failed`
Brevity	Omit articles and filler words	`file too large` not `The file was too large`
Action	Use verb-noun or noun-verb pattern	`config loaded`, `invalid upstream url`

Severity Levels

Level	When to use	Examples
ERROR	Unrecoverable failures requiring attention	`template parse failed`, `listen failed`
WARN	Degraded but recoverable situations	`upstream returned 5xx`, `cache eviction failed`
INFO	Normal business events	`request`, `server started`, `config loaded`
DEBUG	Internal details for troubleshooting	`cache hit`, `rewriting relative url`, `mdx import stripped`

Structured Fields

Use snake_case for field names: upstream_ms, content_type, cache_status
Suffix units: _ms, _bytes, _count
Boolean fields: has_mermaid, has_toc
Avoid embedding data in message string; use fields instead

// Bad
slog.Info(fmt.Sprintf("fetched %s in %dms", url, dur))

// Good
slog.Info("upstream fetched", "upstream", url, "duration_ms", dur)