1 # :zap: zap [![GoDoc][doc-img]][doc] [![Build Status][ci-img]][ci] [![Coverage Status][cov-img]][cov]
3 Blazing fast, structured, leveled logging in Go.
7 `go get -u go.uber.org/zap`
9 Note that zap only supports the two most recent minor versions of Go.
13 In contexts where performance is nice, but not critical, use the
14 `SugaredLogger`. It's 4-10x faster than other structured logging
15 packages and includes both structured and `printf`-style APIs.
18 logger, _ := zap.NewProduction()
19 defer logger.Sync() // flushes buffer, if any
20 sugar := logger.Sugar()
21 sugar.Infow("failed to fetch URL",
22 // Structured context as loosely typed key-value pairs.
25 "backoff", time.Second,
27 sugar.Infof("Failed to fetch URL: %s", url)
30 When performance and type safety are critical, use the `Logger`. It's even
31 faster than the `SugaredLogger` and allocates far less, but it only supports
35 logger, _ := zap.NewProduction()
37 logger.Info("failed to fetch URL",
38 // Structured context as strongly typed Field values.
39 zap.String("url", url),
40 zap.Int("attempt", 3),
41 zap.Duration("backoff", time.Second),
45 See the [documentation][doc] and [FAQ](FAQ.md) for more details.
49 For applications that log in the hot path, reflection-based serialization and
50 string formatting are prohibitively expensive — they're CPU-intensive
51 and make many small allocations. Put differently, using `encoding/json` and
52 `fmt.Fprintf` to log tons of `interface{}`s makes your application slow.
54 Zap takes a different approach. It includes a reflection-free, zero-allocation
55 JSON encoder, and the base `Logger` strives to avoid serialization overhead
56 and allocations wherever possible. By building the high-level `SugaredLogger`
57 on that foundation, zap lets users *choose* when they need to count every
58 allocation and when they'd prefer a more familiar, loosely typed API.
60 As measured by its own [benchmarking suite][], not only is zap more performant
61 than comparable structured logging packages — it's also faster than the
62 standard library. Like all benchmarks, take these with a grain of salt.<sup
63 id="anchor-versions">[1](#footnote-versions)</sup>
65 Log a message and 10 fields:
67 {{.BenchmarkAddingFields}}
69 Log a message with a logger that already has 10 fields of context:
71 {{.BenchmarkAccumulatedContext}}
73 Log a static string, without any context or `printf`-style templating:
75 {{.BenchmarkWithoutFields}}
77 ## Development Status: Stable
79 All APIs are finalized, and no breaking changes will be made in the 1.x series
80 of releases. Users of semver-aware dependency management systems should pin
85 We encourage and support an active, healthy community of contributors —
86 including you! Details are in the [contribution guide](CONTRIBUTING.md) and
87 the [code of conduct](CODE_OF_CONDUCT.md). The zap maintainers keep an eye on
88 issues and pull requests, but you can also report any negative conduct to
89 oss-conduct@uber.com. That email list is a private, safe space; even the zap
90 maintainers don't have access, so don't hesitate to hold us to a high
95 Released under the [MIT License](LICENSE.txt).
97 <sup id="footnote-versions">1</sup> In particular, keep in mind that we may be
98 benchmarking against slightly older versions of other packages. Versions are
99 pinned in zap's [glide.lock][] file. [↩](#anchor-versions)
101 [doc-img]: https://godoc.org/go.uber.org/zap?status.svg
102 [doc]: https://godoc.org/go.uber.org/zap
103 [ci-img]: https://travis-ci.org/uber-go/zap.svg?branch=master
104 [ci]: https://travis-ci.org/uber-go/zap
105 [cov-img]: https://codecov.io/gh/uber-go/zap/branch/master/graph/badge.svg
106 [cov]: https://codecov.io/gh/uber-go/zap
107 [benchmarking suite]: https://github.com/uber-go/zap/tree/master/benchmarks
108 [glide.lock]: https://github.com/uber-go/zap/blob/master/glide.lock