knurling-rs/defmt

Health v2 · maintenance only

Adoption not part of the score

1218 stars · 132 forks observed · 2026-09-03

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-30, confidence not recorded

defmt is a highly efficient logging framework for Rust targeting resource-constrained embedded devices like microcontrollers. It uses deferred formatting and compile-time string compression so the target sends compact binary data while formatting happens on the host machine.

Use cases

• log messages from a microcontroller with minimal flash and bandwidth overhead
• send embedded logs over RTT, ITM, or semihosting to a host PC
• decode and print defmt-encoded logs on the host
• filter log levels at compile time with module-level granularity
• run tests on-target with formatted output
• send panic messages from firmware to a debugger

When to choose

• you're writing Rust firmware for a microcontroller and need fast, low-overhead logging
• your target has no display and logs must be transferred to a host machine
• you want compile-time log filtering and compact string encoding
• you need on-target test and panic reporting integrated with your logger

When to avoid

• you're logging on a host platform like a web server where standard loggers suffice
• your firmware output format isn't ELF or you can't customize linker scripts
• you need multiple independent global logger instances
• you're not using Rust

Facets

library · maturity active

logging serialization cli testing embedded-systems developer-tools embedded rust cli cross-platform deferred-formatting microcontrollers rtt itm semihosting panic-handler on-target-testing string-compression rust

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