:zap: zap 
Blazing fast, structured, leveled logging in Go.
Installation
go get -u go.uber.org/zap
Note that zap only supports the two most recent minor versions of Go.
Quick Start
In contexts where performance is nice, but not critical, use the
SugaredLogger. It's 4-10x faster than other structured logging
packages and includes both structured and printf-style APIs.
logger, _ := zap.NewProduction()
defer logger.Sync() // flushes buffer, if any
sugar := logger.Sugar()
sugar.Infow("failed to fetch URL",
// Structured context as loosely typed key-value pairs.
"url", url,
"attempt", 3,
"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, _ := zap.NewProduction()
defer logger.Sync()
logger.Info("failed to fetch URL",
// Structured context as strongly typed Field values.
zap.String("url", url),
zap.Int("attempt", 3),
zap.Duration("backoff", time.Second),
)
See the documentation and FAQ for more details.
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 packages — 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:
| Package | Time | Time % to zap | Objects Allocated |
|---|---|---|---|
| :zap: zap | 2900 ns/op | +0% | 5 allocs/op |
| :zap: zap (sugared) | 3475 ns/op | +20% | 10 allocs/op |
| zerolog | 10639 ns/op | +267% | 32 allocs/op |
| go-kit | 14434 ns/op | +398% | 59 allocs/op |
| logrus | 17104 ns/op | +490% | 81 allocs/op |
| apex/log | 32424 ns/op | +1018% | 66 allocs/op |
| log15 | 33579 ns/op | +1058% | 76 allocs/op |
Log a message with a logger that already has 10 fields of context:
| Package | Time | Time % to zap | Objects Allocated |
|---|---|---|---|
| :zap: zap | 373 ns/op | +0% | 0 allocs/op |
| :zap: zap (sugared) | 452 ns/op | +21% | 1 allocs/op |
| zerolog | 288 ns/op | -23% | 0 allocs/op |
| go-kit | 11785 ns/op | +3060% | 58 allocs/op |
| logrus | 19629 ns/op | +5162% | 70 allocs/op |
| log15 | 21866 ns/op | +5762% | 72 allocs/op |
| apex/log | 30890 ns/op | +8182% | 55 allocs/op |
Log a static string, without any context or printf-style templating:
| Package | Time | Time % to zap | Objects Allocated |
|---|---|---|---|
| :zap: zap | 381 ns/op | +0% | 0 allocs/op |
| :zap: zap (sugared) | 410 ns/op | +8% | 1 allocs/op |
| zerolog | 369 ns/op | -3% | 0 allocs/op |
| standard library | 385 ns/op | +1% | 2 allocs/op |
| go-kit | 606 ns/op | +59% | 11 allocs/op |
| logrus | 1730 ns/op | +354% | 25 allocs/op |
| apex/log | 1998 ns/op | +424% | 7 allocs/op |
| log15 | 4546 ns/op | +1093% | 22 allocs/op |
Development Status: Stable
All APIs are finalized, and no breaking changes will be made in the 1.x series
of releases. Users of semver-aware dependency management systems should pin
zap to ^1.
Contributing
We encourage and support an active, healthy community of contributors —
including you! Details are in the contribution guide and
the code of conduct. The zap maintainers keep an eye on
issues and pull requests, but you can also report any negative conduct to
oss-conduct@uber.com. That email list is a private, safe space; even the zap
maintainers don't have access, so don't hesitate to hold us to a high
standard.
Released under the MIT License.
1 In particular, keep in mind that we may be
benchmarking against slightly older versions of other packages. Versions are
pinned in the benchmarks/go.mod file. ↩