zerolog

Zerolog, commonly written zerolog, is an open-source, high-performance structured logging library for the Go programming language. It is designed to minimize runtime overhead and to produce machine-parsable logs by default. The library emits structured events in JSON by default, enabling easy ingestion by log analytics systems, while also offering a ConsoleWriter for human-readable output during development.

Zerolog provides a fluent, chainable API for building log events. It supports multiple log levels (Debug, Info, Warn, Error, Fatal, Panic) and a variety of typed fields (Str, Int, Bool, Time, Dur, etc.). Loggers can be extended with context-specific fields using the With method, producing derived loggers that carry additional metadata. Messages are emitted with Msg and can be augmented with fields created along the chain; Errors can be logged with Err(err) alongside a message.

Output destinations can be configured using Output to an io.Writer, and the library includes ConsoleWriter to render text logs. Time field format can be customized (TimeFieldFormat). Zerolog is designed to minimize allocations during logging, which makes it suitable for high-throughput services, often used in microservices and cloud-native environments.

The project is open-source and released under the MIT license. It is widely used in Go projects requiring structured logging, and its API emphasizes simplicity and performance, with integrations for the standard library and ecosystem tooling.