⚡ zap

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:

{{.BenchmarkAddingFields}}

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

{{.BenchmarkAccumulatedContext}}

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

{{.BenchmarkWithoutFields}}

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
[email protected]. 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.

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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. ↩