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Clojure(Script) logging & profiling library

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[com.taoensso/timbre "4.1.1"] ; Stable, see CHANGELOG for details
[com.taoensso/timbre "3.4.0"] ; Legacy

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.

Getting started


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

[com.taoensso/timbre "4.1.1"] ; 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).


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.

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