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Pure Clojure/Script logging library
Latest commit ba6bc3f Jun 29, 2016 @ptaoussanis v4.5.1

Taoensso open-source

CHANGELOG | API | current Break Version:

[com.taoensso/timbre "4.5.1"] ; Stable

Please consider helping to support my continued open-source Clojure/Script work?

Even small contributions can add up + make a big difference to help sustain my time writing, maintaining, and supporting Timbre and other Clojure/Script libraries. Thank you!

- Peter Taoussanis


A pure Clojure/Script logging library

Java logging is a Kafkaesque mess of complexity that buys you nothing. It can be comically hard to get even the simplest logging working, and it just gets worse at scale.

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

Supports optional interop with tools.logging and log4j/logback/slf4j.

Happy hacking!


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

3rd-party tools, appenders, etc.

Link Description
@fzakaria/slf4j-timbre Route log4j/logback/sfl4j log output to Timbre
@palletops/log-config Library to help manage Timbre logging config
Your link here? PR's welcome!

Getting started

Add the necessary dependency to your project:

[com.taoensso/timbre "4.5.1"]

And setup your namespace imports:

(ns my-clj-ns ; Clojure namespace
    [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 p defnp profile)]))

(ns my-cljs-ns ; ; ClojureScript namespace
    [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 call (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 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 {}})

And/or you can set the TIMBRE_DEFAULT_STACKTRACE_FONTS environment variable (supports edn).


This is the biggest win over Java logging IMO. All of Timbre's behaviour is controlled through a single, simple Clojure map.

See timbre/example-config for Timbre's default config map

(def example-config
  "An example 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 (clj only)
      :rate-limit      ; [[ncalls-limit window-ms] <...>], or nil
      :output-fn       ; Optional override for inherited (fn [data]) -> string
      :timestamp-opts  ; Optional override for inherited {:pattern _ :locale _ :timezone _}
      :ns-whitelist    ; Optional, stacks with active config's whitelist
      :ns-blacklist    ; Optional, stacks with active config's blacklist
      :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
      :?line           ; Integer, or nil ; Waiting on CLJ-865
      :?err            ; First-arg platform error, or nil
      :vargs           ; Vector of raw args
      :output_         ; Forceable - final formatted output string created
                       ; by calling (output-fn <this-data-map>)
      :msg_            ; Forceable - args as a string
      :timestamp_      ; Forceable - string
      :hostname_       ; Forceable - string (clj only)
      :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

      **NB** - any keys not specifically documented here should be
      considered private / subject to change without notice.

    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 dispatch 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

   {;; The standard println appender:
    ;; :println (println-appender {:stream :auto})

    ;; Inline 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 [data]) -> side effects
     (fn [data]
       (let [{:keys [output_]} data
             formatted-output-str (force output_)]
         (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 <latest-version>] ; 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).
  • Configurable number of entries to keep per log level.
  • Only the most recent instance of each unique entry is kept.
  • Resulting log is just a Clojure value: a vector of log entries (maps).

Clojure has a rich selection of built-in and 3rd party tools for querying values like this.

See also car-appender/query-entries.

Email (Postal) appender

;; [com.draines/postal <latest-version>] ; 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. Thanks goes to the respective authors!

Just give me a shout if you've got an appender you'd like to have added.


Currently Clj only

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

And these can certainly do the job. But as with many Java tools, they can be a little hairy and often heavy-handed. Timbre includes a simple, lightweight 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

Timbre profiling is 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.

See also defnp, sampling-profile.

This project supports the ClojureWerkz-logo goals

ClojureWerkz is a growing collection of open-source, batteries-included Clojure libraries that emphasise modern targets, great documentation, and thorough testing.

Contacting me / contributions

Please use the project's GitHub issues page for all questions, ideas, etc. Pull requests welcome. See the project's GitHub contributors page for a list of contributors.

Otherwise, you can reach me at Happy hacking!

- Peter Taoussanis


Distributed under the EPL v1.0 (same as Clojure).
Copyright © 2015-2016 Peter Taoussanis.

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