#defmt #no-std #logging

no-std defmt-or-log

Logging macros that forward to either defmt or log

3 unstable releases

0.2.0 Nov 20, 2023
0.1.1 Nov 20, 2023
0.1.0 Nov 20, 2023

#435 in Embedded development

Download history 140/week @ 2023-11-18 64/week @ 2023-11-25 25/week @ 2023-12-02

229 downloads per month


244 lines


In embedded projects you often want to log something either via core::fmt::Debug or defmt::Format, depending on the configuration. The crate defmt-or-log provides the usual logger macros and either forwards them to the log or defmt crate, depending on the enabled features.

Furthermore, the defmt-or-log crate provides:

  • the FormatOrDebug trait, that uses core::fmt::Debug or defmt::Format as super-trait and provides matching blanket implementations. This is useful for specifying trait bounds.
  • the Debug2Format struct, which behaves similar to defmt::Debug2Format, but does nothing extra if using log.

See examples/derive.rs.

You may either enable the log or the defmt feature but not both.
The feature at_least_one (enabled per default) generates a compiler error if neither log nor defmt are enabled.

This repository, also provides the defmt-or-log-macros crate, which Proc Macros to conditonally derive core::fmt::Debug or defmt::Format, depending on the enabled features.

Supported macros (defmt-or-log crate):

  • trace

  • debug

  • info

  • warn

  • error

  • assert

  • assert_eq

  • assert_ne

  • debug_assert

  • debug_assert_eq

  • debug_assert_ne

  • todo

  • unreachable

  • panic

  • unwrap


Licensed under either of:

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.