⚡ zap

Blazing fast, structured, leveled logging in Go.

Installation

go get -u go.uber.org/zap

Quick Start

In contexts where performance is nice, but not critical, use the SugaredLogger. It's 4-10x faster than than other structured logging libraries and includes both structured and printf-style APIs.

logger, _ := NewProduction()
sugar := logger.Sugar()
sugar.Infow("Failed to fetch URL.",
  // Structured context as loosely-typed key-value pairs.
  "url", url,
  "attempt", retryNum,
  "backoff", time.Second,
)
sugar.Infof("Failed to fetch URL: %s", url)

When performance and type safety are critical, use the Logger. It's even faster than the SugaredLogger and allocates far less, but it only supports structured logging.

logger, _ := NewProduction()
logger.Info("Failed to fetch URL.",
  // Structured context as strongly-typed Field values.
  zap.String("url", url),
  zap.Int("attempt", tryNum),
  zap.Duration("backoff", time.Second),
)

Performance

For applications that log in the hot path, reflection-based serialization and string formatting are prohibitively expensive — they're CPU-intensive and make many small allocations. Put differently, using encoding/json and fmt.Fprintf to log tons of interface{}s makes your application slow.

Zap takes a different approach. It includes a reflection-free, zero-allocation JSON encoder, and the base Logger strives to avoid serialization overhead and allocations wherever possible. By building the high-level SugaredLogger on that foundation, zap lets users choose when they need to count every allocation and when they'd prefer a more familiar, loosely-typed API.

As measured by its own benchmarking suite, not only is zap more performant than comparable structured logging libraries — it's also faster than the standard library. Like all benchmarks, take these with a grain of salt.¹

Log a message and 10 fields:

Library	Time	Bytes Allocated	Objects Allocated
⚡ zap	1436 ns/op	705 B/op	2 allocs/op
⚡ zap (sugared)	2436 ns/op	1931 B/op	21 allocs/op
logrus	9393 ns/op	5783 B/op	77 allocs/op
go-kit	6929 ns/op	3119 B/op	65 allocs/op
log15	25004 ns/op	5535 B/op	91 allocs/op
apex/log	18450 ns/op	4025 B/op	64 allocs/op

Log a message with a logger that already has 10 fields of context:

Library	Time	Bytes Allocated	Objects Allocated
⚡ zap	368 ns/op	0 B/op	0 allocs/op
⚡ zap (sugared)	388 ns/op	0 B/op	0 allocs/op
logrus	8420 ns/op	3967 B/op	61 allocs/op
go-kit	7288 ns/op	2950 B/op	50 allocs/op
log15	17678 ns/op	2546 B/op	42 allocs/op
apex/log	16126 ns/op	2801 B/op	49 allocs/op

Log a static string, without any context or printf-style templating:

Library	Time	Bytes Allocated	Objects Allocated
⚡ zap	398 ns/op	0 B/op	0 allocs/op
⚡ zap (sugared)	400 ns/op	80 B/op	2 allocs/op
standard library	678 ns/op	80 B/op	2 allocs/op
logrus	2778 ns/op	1409 B/op	25 allocs/op
go-kit	1318 ns/op	656 B/op	13 allocs/op
log15	5720 ns/op	1496 B/op	24 allocs/op
apex/log	3282 ns/op	584 B/op	11 allocs/op

Development Status: Release Candidate 2

The current release is v1.0.0-rc.2. No further breaking changes are planned unless wider use reveals critical bugs or usability issues, but users who need absolute stability should wait for the 1.0.0 release.

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Released under the [MIT License](LICENSE.txt).

¹ In particular, keep in mind that we may be benchmarking against slightly older versions of other libraries. Versions are pinned in zap's glide.lock file. ↩