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[com.taoensso/timbre "4.1.4"] ; Stable, see CHANGELOG for details

Timbre, a (sane) Clojure/Script logging & profiling library

Java logging is a mess of complexity that buys you nothing. It can be comically hard to get even the simplest logging working, and it's no better at scale.

Timbre offers an all Clojure/Script alternative that works out the box. It's fast, deeply flexible, and easy to configure. No XML!

What's in the box™?

  • Full Clojure + ClojureScript support (v4+)
  • No XML or properties files. A single, simple config map, and you're set
  • Deeply flexible fn appender model with middleware
  • Great performance at any scale
  • Filter logging by levels and namespace whitelist/blacklist patterns
  • Zero overhead with complete Clj+Cljs elision for compile-time level/ns filters
  • Useful built-in appenders for out-the-box Clj+Cljs logging
  • Powerful, easy-to-configure per-appender rate limits and async logging
  • Logs as Clojure values (v3+)
  • tools.logging support (optional, useful when integrating with legacy logging systems)
  • Level and ns-filter aware logging profiler
  • Tiny, simple, cross-platform codebase

3rd-party tools, appenders, etc.

  • log-config by Hugo Duncan - library to help manage Timbre logging config.
  • slf4j-timbre - Timbre all the things! Ever frustrated by having to maintain a log4j/logback/sfl4j configuration for your Java dependencies? Have them all route to Timbre!
  • Other suggestions welcome!

Getting started


Add the necessary dependency to your Leiningen project.clj and require the necessary namespaces:

[com.taoensso/timbre "4.1.4"] ; Add to your project.clj :dependencies

(ns my-clj-ns ; Clj ns => use `:refer`
    [taoensso.timbre :as timbre
      :refer (log  trace  debug  info  warn  error  fatal  report
              logf tracef debugf infof warnf errorf fatalf reportf
              spy get-env log-env)]
    [taoensso.timbre.profiling :as profiling
      :refer (pspy pspy* profile defnp p p*)]))

(ns my-cljs-ns ; Cljs ns => use `:refer-macros`
    [taoensso.timbre :as timbre
      :refer-macros (log  trace  debug  info  warn  error  fatal  report
                     logf tracef debugf infof warnf errorf fatalf reportf
                     spy get-env log-env)]))

You can also use timbre/refer-timbre to configure Clj ns referrals automatically


By default, Timbre gives you basic println and js/console (v4+) output at a :debug log level:

(info "This will print") => nil
%> 15-Jun-13 19:18:33 localhost INFO [my-app.core] - This will print

(spy :info (* 5 4 3 2 1)) => 120
%> 15-Jun-13 19:19:13 localhost INFO [my-app.core] - (* 5 4 3 2 1) => 120

(defn my-mult [x y] (info "Lexical env:" (get-env)) (* x y)) => #'my-mult
(my-mult 4 7) => 28
%> 15-Jun-13 19:21:53 localhost INFO [my-app.core] - Lexical env: {x 4, y 7}

(trace "This won't print due to insufficient log level") => nil

First-argument exceptions generate a nicely cleaned-up stack trace using io.aviso.exception (Clj only):

(info (Exception. "Oh noes") "arg1" "arg2")
%> 15-Jun-13 19:22:55 localhost INFO [my-app.core] - arg1 arg2
java.lang.Exception: On noes

Other utils include: log-errors, log-and-rethrow-errors, logged-future, and handle-uncaught-jvm-exceptions! (please see the API docs for details).

Disabling stacktrace colors

ANSI colors are enabled by default for stacktraces. To turn these off (e.g. for log files or emails), you can add the following entry to your top-level config or individual appender map/s:

:output-fn (partial timbre/default-output-fn {:stacktrace-fonts {}})


This is the biggest win over Java logging IMO. Here's timbre/example-config (also Timbre's default config):

The example below shows config for Timbre v4. See here for an example of Timbre v3 config.

(def example-config
  "Example (+default) Timbre v4 config map.

    An appender is a map with keys:
      :min-level       ; Level keyword, or nil (=> no minimum level)
      :enabled?        ;
      :async?          ; Dispatch using agent? Useful for slow appenders
      :rate-limit      ; [[ncalls-limit window-ms] <...>], or nil
      :output-fn       ; Optional override for inherited (fn [data]) -> string
      :fn              ; (fn [data]) -> side effects, with keys described below

    An appender's fn takes a single data map with keys:
      :config          ; Entire config map (this map, etc.)
      :appender-id     ; Id of appender currently dispatching
      :appender        ; Entire map of appender currently dispatching

      :instant         ; Platform date (java.util.Date or js/Date)
      :level           ; Keyword
      :error-level?    ; Is level e/o #{:error :fatal}?
      :?ns-str         ; String, or nil
      :?file           ; String, or nil  ; Waiting on CLJ-865
      :?line           ; Integer, or nil ; Waiting on CLJ-865

      :?err_           ; Delay - first-arg platform error, or nil
      :vargs_          ; Delay - raw args vector
      :hostname_       ; Delay - string (clj only)
      :msg_            ; Delay - args string
      :timestamp_      ; Delay - string
      :output-fn       ; (fn [data]) -> formatted output string
                       ; (see `default-output-fn` for details)

      :context         ; *context* value at log time (see `with-context`)
      :profile-stats   ; From `profile` macro

    Middleware are simple (fn [data]) -> ?data fns (applied left->right) that
    transform the data map dispatched to appender fns. If any middleware returns
    nil, NO dispatching will occur (i.e. the event will be filtered).

  The `example-config` source code contains further settings and details.
  See also `set-config!`, `merge-config!`, `set-level!`."

  {:level :debug  ; e/o #{:trace :debug :info :warn :error :fatal :report}

   ;; Control log filtering by namespaces/patterns. Useful for turning off
   ;; logging in noisy libraries, etc.:
   :ns-whitelist  [] #_[""]
   :ns-blacklist  [] #_["taoensso.*"]

   :middleware [] ; (fns [data]) -> ?data, applied left->right

   ;; Clj only:
   :timestamp-opts default-timestamp-opts ; {:pattern _ :locale _ :timezone _}

   :output-fn default-output-fn ; (fn [data]) -> string

   {:example-println-appender ; Appender id
     ;; Appender definition (just a map):
     {:enabled?   true
      :async?     false
      :min-level  nil
      :rate-limit [[1 250] [10 5000]] ; 1/250ms, 10/5s
      :output-fn  :inherit
      :fn ; Appender's fn
      (fn [data]
        (let [{:keys [output-fn]} data
              formatted-output-str (output-fn data)]
          (println formatted-output-str)))}}})

A few things to note:

  • Appenders are trivial to write & configure - they're just fns. It's Timbre's job to dispatch useful args to appenders when appropriate, it's their job to do something interesting with them.
  • Being 'just fns', appenders have basically limitless potential: write to your database, send a message over the network, check some other state (e.g. environment config) before making a choice, etc.

Log levels and ns filters

The log level may be set:

  • At compile-time: (TIMBRE_LEVEL environment variable).
  • Statically using: timbre/set-level!/timbre/merge-level!.
  • Dynamically using: timbre/with-level.

The ns filters may be set:

  • At compile-time: (TIMBRE_NS_WHITELIST, TIMBRE_NS_BLACKLIST env vars).
  • Statically using: timbre/set-config!/timbre/merge-config!.
  • Dynamically using: timbre/with-config.

There are also variants of the core logging macros that take an explicit config arg:

(timbre/log*  <config-map> <level> <& args>) ; or
(timbre/logf* <config-map> <level> <& args>)

Logging calls excluded by a compile-time option (e.g. during Cljs compilation) will be entirely elided from your codebase, e.g.:


# edn values welcome:
export TIMBRE_LEVEL=':warn'               # Elide all lower logging calls
export TIMBRE_NS_WHITELIST='["my-app.*"]' # Elide all other ns logging calls
export TIMBRE_NS_BLACKLIST='["" "*"]'

lein cljsbuild once # Compile js with appropriate logging calls excluded
lein uberjar        # Compile jar ''

Built-in appenders

Redis (Carmine) appender (v3+)

;; [com.taoensso/carmine "2.10.0"] ; Add to project.clj deps
;; (:require [taoensso.timbre.appenders (carmine :as car-appender)]) ; Add to ns

(timbre/merge-config! {:appenders {:carmine (car-appender/carmine-appender)}})

This gives us a high-performance Redis appender:

  • All raw logging args are preserved in serialized form (even errors!).
  • Only the most recent instance of each unique entry is kept (hash fn used to determine uniqueness is configurable).
  • Configurable number of entries to keep per log level.
  • Log is just a value: a vector of Clojure maps: query+manipulate with standard seq fns: group-by hostname, sort/filter by ns & severity, explore exception stacktraces, filter by raw arguments, stick into or query with Datomic, etc.

A simple query utility is provided: car-appender/query-entries.

Email (Postal) appender

;; [com.draines/postal "1.11.3"] ; Add to project.clj deps
;; (:require [taoensso.timbre.appenders (postal :as postal-appender)]) ; Add to ns

      ^{:host "" :user "jsmith" :pass "sekrat!!1"}
      {:from "" :to ""})}})

File appender

;; (:require [taoensso.timbre.appenders.core :as appenders]) ; Add to ns

  {:appenders {:spit (appenders/spit-appender {:fname "/path/my-file.log"})}})

Other included appenders

A number of 3rd-party appenders are included out-the-box here. Please see the relevant docstring for details. Thank you to the respective authors! Just give me a shout if you've got an appender you'd like to have added.

Profiling (currently Clj only)

The usual recommendation for Clojure profiling is: use a good JVM profiler like YourKit, JProfiler, or VisualVM.

And these certainly do the job. But as with many Java tools, they can be a little hairy and often heavy-handed - especially when applied to Clojure. Timbre includes an alternative.

Wrap forms that you'd like to profile with the p macro and give them a name:

(defn my-fn
  (let [nums (vec (range 1000))]
    (+ (p :fast-sleep (Thread/sleep 1) 10)
       (p :slow-sleep (Thread/sleep 2) 32)
       (p :add  (reduce + nums))
       (p :sub  (reduce - nums))
       (p :mult (reduce * nums))
       (p :div  (reduce / nums)))))

(my-fn) => 42

The profile macro can now be used to log times for any wrapped forms:

(profile :info :Arithmetic (dotimes [n 100] (my-fn))) => "Done!"
%> 2012-Jul-03 20:46:17 +0700 localhost INFO [my-app] - Profiling my-app/Arithmetic
              Name  Calls       Min        Max       MAD      Mean  Total% Total
 my-app/slow-sleep    100       2ms        2ms      31μs       2ms      57 231ms
 my-app/fast-sleep    100       1ms        1ms      27μs       1ms      29 118ms
        my-app/add    100      44μs        2ms      46μs     100μs       2 10ms
        my-app/sub    100      42μs      564μs      26μs      72μs       2 7ms
        my-app/div    100      54μs      191μs      17μs      71μs       2 7ms
       my-app/mult    100      31μs      165μs      11μs      44μs       1 4ms
       Unaccounted                                                       6 26ms
             Total                                                     100 405ms

You can also use the defnp macro to conveniently wrap whole fns.

Timbre profiling is fully log level & ns filter aware: if the level is insufficient or ns filtered, you won't pay for profiling.

And since p and profile always return their body's result, it becomes feasible to use profiling more often as part of your normal workflow: just leave profiling code in production as you do logging code.

A simple sampling profiler is also included.

This project supports the CDS and ClojureWerkz goals

  • CDS, the Clojure Documentation Site, is a contributer-friendly community project aimed at producing top-notch, beginner-friendly Clojure tutorials and documentation. Awesome resource.

  • ClojureWerkz is a growing collection of open-source, batteries-included Clojure libraries that emphasise modern targets, great documentation, and thorough testing. They've got a ton of great stuff, check 'em out!

Contact & contributing

lein start-dev to get a (headless) development repl that you can connect to with Cider (Emacs) or your IDE.

Please use the project's GitHub issues page for project questions/comments/suggestions/whatever (pull requests welcome!). Am very open to ideas if you have any!

Otherwise reach me (Peter Taoussanis) at or on Twitter. Cheers!


Copyright © 2012-2015 Peter Taoussanis. Distributed under the Eclipse Public License, the same as Clojure.