/golang-samber-slog

name: golang-samber-slog
description: "Structured logging extensions for Golang using samber/slog-**** packages — multi-handler pipelines (slog-multi), log sampling (slog-sampling), attribute formatting (slog-formatter), HTTP middleware (slog-fiber, slog-gin, slog-chi, slog-echo), and backend routing (slog-datadog, slog-sentry, slog-loki, slog-syslog, slog-logstash, slog-graylog...). Apply when using or adopting slog, or when the codebase already imports any github.com/samber/slog-* package."
user-invocable: true
license: MIT
compatibility: Designed for Claude Code, Codex or similar harness, and for projects using Golang.
metadata:
  author: samber
  version: "1.1.2"
  openclaw:
    emoji: "🪵"
    homepage: https://github.com/samber/cc-skills-golang
    requires:
      bins:
        - go
    install: []
    skill-library-version:
      slog-multi: "1.8.0"
      slog-sampling: "1.6.0"
      slog-formatter: "1.3.0"
      slog-fiber: "1.22.1"
      slog-gin: "1.21.0"
      slog-chi: "1.19.0"
      slog-echo: "1.21.0"
      slog-http: "1.12.0"
      slog-betterstack: "1.4.4"
      slog-channel: "1.4.4"
      slog-datadog: "2.10.4"
      slog-sentry: "2.10.3"
      slog-loki: "3.7.2"
      slog-syslog: "2.5.4"
      slog-logstash: "2.6.4"
      slog-graylog: "2.7.5"
      slog-fluentd: "2.5.4"
      slog-kafka: "2.6.5"
      slog-logrus: "2.5.4"
      slog-zap: "2.6.4"
      slog-zerolog: "2.9.2"
      slog-slack: "2.7.5"
      slog-telegram: "2.4.4"
      slog-webhook: "2.8.4"
      slog-mattermost: "2.5.4"
      slog-microsoft-teams: "2.7.4"
      slog-nats: "0.4.5"
      slog-otel: "0.1.0"
      slog-parquet: "2.5.2"
      slog-quickwit: "0.3.4"
      slog-rollbar: "2.7.4"
      slog-mock: "0.1.0"
allowed-tools: Read Edit Write Glob Grep Bash(go:*) Bash(golangci-lint:*) Bash(git:*) Agent WebFetch mcp__context7__resolve-library-id mcp__context7__query-docs AskUserQuestion Bash(godig:*) Bash(gopls:*) LSP mcp__gopls__*
paths:
  - "**/*.go"

**Persona:** You are a Go logging architect. You design log pipelines where every record flows through the right handlers — sampling drops noise early, formatters strip PII before records leave the process, and routers send errors to Sentry while info goes to Loki.

samber/slog-\*\*\*\* — Structured Logging Pipeline for Go

20+ composable `slog.Handler` packages for Go 1.21+. Three core pipeline libraries plus HTTP middlewares and backend sinks that all implement the standard `slog.Handler` interface.

**Official resources:**

• [github.com/samber/slog-multi](https://github.com/samber/slog-multi) — handler composition
• [github.com/samber/slog-sampling](https://github.com/samber/slog-sampling) — throughput control
• [github.com/samber/slog-formatter](https://github.com/samber/slog-formatter) — attribute transformation

This skill is not exhaustive — refer to library documentation and code examples for more information:

• For Go package docs, symbols, versions, importers, and known vulnerabilities, → See `samber/cc-skills-golang@golang-pkg-go-dev` skill (`godig`), preferred over Context7 for Go package facts.
• To navigate this library's usage in your own code (definitions, call sites, diagnostics), → See `samber/cc-skills-golang@golang-gopls` skill (`gopls`).
• Context7 remains a fallback for docs not indexed on pkg.go.dev.

The Pipeline Model

Every samber/slog pipeline follows a canonical ordering. Records flow left to right — place sampling first to drop early and avoid wasting CPU on records that never reach a sink.

record → [Sampling] → [Pipe: trace/PII] → [Router] → [Sinks]

Order matters: sampling before formatting saves CPU. Formatting before routing ensures all sinks receive clean attributes. Reversing this wastes work on records that get dropped.

Core Libraries

| Library | Purpose | Key constructors | | --- | --- | --- | | `slog-multi` | Handler composition | `Fanout`, `Router`, `FirstMatch`, `Failover`, `Pool`, `Pipe` | | `slog-sampling` | Throughput control | `UniformSamplingOption`, `ThresholdSamplingOption`, `AbsoluteSamplingOption`, `CustomSamplingOption` | | `slog-formatter` | Attribute transforms | `PIIFormatter`, `ErrorFormatter`, `FormatByType[T]`, `FormatByKey`, `FlattenFormatterMiddleware` |

slog-multi — Handler Composition

Six composition patterns, each for a different routing need:

| Pattern | Behavior | Latency impact | | --- | --- | --- | | `Fanout(handlers...)` | Broadcast to all handlers sequentially | Sum of all handler latencies | | `Router().Add(h, predicate).Handler()` | Route to ALL matching handlers | Sum of matching handlers | | `Router().Add(...).FirstMatch().Handler()` | Route to FIRST match only | Single handler latency | | `Failover()(handlers...)` | Try sequentially until one succeeds | Primary handler latency (happy path) | | `Pool()(handlers...)` | Load-balance: sends each record to ONE handler | Single handler latency | | `Pipe(middlewares...).Handler(sink)` | Middleware chain before sink | Middleware overhead + sink |

// Route errors to Sentry, all logs to stdout
logger := slog.New(
    slogmulti.Router().
        Add(sentryHandler, slogmulti.LevelIs(slog.LevelError)).
        Add(slog.NewJSONHandler(os.Stdout, nil)).
        Handler(),
)

Built-in predicates: `LevelIs`, `LevelIsNot`, `MessageIs`, `MessageIsNot`, `MessageContains`, `MessageNotContains`, `AttrValueIs`, `AttrKindIs`.

For full code examples of every pattern, see [Pipeline Patterns](references/pipeline-patterns.md).

slog-sampling — Throughput Control

| Strategy | Behavior | Best for | | --- | --- | --- | | Uniform | Drop fixed % of all records | Dev/staging noise reduction | | Threshold | Log first N per interval, then sample at rate R | Production — preserves initial visibility | | Absolute | Cap at N records per interval globally | Hard cost control | | Custom | User function returns sample rate per record | Level-aware or time-aware rules |

Sampling MUST be the outermost handler in the pipeline —