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# :zap: zap [![GoDoc][doc-img]][doc] [![Build Status][ci-img]][ci] [![Coverage Status][cov-img]][cov]
Blazing fast, structured, leveled logging in Go.
## Installation
`go get -u`
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][doc] 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.<sup
Log a message and 10 fields:
Log a message with a logger that already has 10 fields of context:
Log a static string, without any context or `printf`-style templating:
## 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 &mdash;
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 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
Released under the [MIT License](LICENSE.txt).
<sup id="footnote-versions">1</sup> In particular, keep in mind that we may be
benchmarking against slightly older versions of other packages. Versions are
pinned in zap's [glide.lock][] file. [↩](#anchor-versions)
[benchmarking suite]: