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⚡ zap GoDoc Build Status Coverage Status

Fast, structured, leveled logging in Go.

Structure

Zap takes an opinionated stance on logging and doesn't provide any printf-style helpers. Rather than logger.Printf("Error %v writing logs to %v, lost %v messages.", err, f, m), flog encourages the more structured

Logger.
  WithError(err).
  With("msgCount", m).
  With("fileName", f).
  Info("Error writing logs.")

This a bit more verbose, but it enables powerful ad-hoc analysis, flexible dashboarding, and accurate message bucketing. In short, it helps you get the most out of tools like ELK, Splunk, and Sentry. All log messages are JSON-serialized.

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 to log tons of interface{}s makes your application slow.

Zap's API offers a variety of type-safe ways to annotate a logger's context without incurring tons of overhead. It also offers a suite of conditional annotations, so collecting rich debugging context doesn't impact normal operations.

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.

Add 5 fields to the logging context, one at a time:

Library Time Bytes Allocated Objects Allocated
zap 3340 ns/op 5713 B/op 16 allocs/op
logrus 66776 ns/op 52646 B/op 254 allocs/op

Add 5 fields to the logging context as a single map:

Library Time Bytes Allocated Objects Allocated
zap 1615 ns/op 1504 B/op 6 allocs/op
logrus 36592 ns/op 21409 B/op 209 allocs/op

Log static strings, without any context or printf-style formatting:

Library Time Bytes Allocated Objects Allocated
zap 328 ns/op 32 B/op 1 allocs/op
standard library 840 ns/op 592 B/op 2 allocs/op

Development Status: Alpha

Breaking changes are certain.

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