diff --git a/Daeghrefn/Communication.tcl b/Daeghrefn/Communication.tcl
--- a/Daeghrefn/Communication.tcl
+++ b/Daeghrefn/Communication.tcl
@@ -209,6 +209,11 @@
 			}
 		}
 
+		"reconfigure" {
+			twitter_update_short_url_length
+			return 1
+		}
+
 		default { putdcc $idx "Unknown Twitter command: $arg"}
 	}
 }
@@ -336,9 +341,9 @@
 		putquick "NOTICE $nick :Syntaxe : !pub <texte à publier sur identi.ca et Twitter>"
 		return
 	}
-	set len [string length $text]
+	set len [twitter_compute_len $text]
 	if {$len > 140} {
-		putquick "NOTICE $nick :140 caractères max, là il y en a $len."
+		putquick "NOTICE $nick :140 caractères max, là il y en a $len ([twitter_get_short_url_length] par lien)."
 		return
 	}
 	if [twitterpost $account $text] {
@@ -376,6 +381,36 @@
 	twitter_query $url $account "" POST
 }
 
+# @param param The parameter to fetch in the API reply
+# return The value from configuration the JSON document, or a dict if it contains several parameters
+proc twitter_get_configuration_parameter {param} {
+	set account [registry get twitter.default_account]
+	set url https://api.twitter.com/1.1/help/configuration.json
+	set config [twitter_query $url $account]
+	dict get $config $param
+}
+
+proc twitter_update_short_url_length {} {
+	set len [twitter_get_configuration_parameter short_url_length]
+	registry set twitter.short_url_length $len
+}
+
+proc twitter_get_short_url_length {} {
+	registry get twitter.short_url_length
+}
+
+# Computes len of a tweet, taking in consideration t.co URL length
+# See https://dev.twitter.com/basics/tco
+proc twitter_compute_len {text} {
+	set short_url_length [twitter_get_short_url_length]
+
+	set len [strlen $text]
+	foreach url [geturls $text] {
+		incr len [expr $short_url_length - [strlen $url]]
+	}
+	return $len
+}
+
 #
 # Mail
 #
diff --git a/tests/Communication.test b/tests/Communication.test
new file mode 100644
--- /dev/null
+++ b/tests/Communication.test
@@ -0,0 +1,40 @@
+package require tcltest
+namespace import ::tcltest::*
+
+###
+### Init
+###
+
+# Tested code
+source init.tcl
+source $dir/Daeghrefn/Communication.tcl
+
+###
+### Mocks
+###
+
+# This value is normally given by a cached value in the registry
+# and updated through an API call to /help/configuration.json.
+proc twitter_get_short_url_length {} { return 23 }
+
+###
+### Tests
+###
+
+test twitter_compute_len_empty {} -body {
+	twitter_compute_len ""
+} -result 0
+
+test twitter_compute_len_regular_string {} -body {
+	twitter_compute_len "quux"
+} -result 4
+
+test twitter_compute_len_links {} -body {
+	twitter_compute_len "Je vais sur http://www.perdu.com pour y lire https://fr.wikipedia.org/w/index.php?title=Les_B%C3%A2tards_du_Nord&type=revision&diff=133589772&oldid=133589631"
+} -result 71
+
+###
+### Cleanup
+###
+
+cleanupTests
diff --git a/tests/init.tcl b/tests/init.tcl
--- a/tests/init.tcl
+++ b/tests/init.tcl
@@ -13,3 +13,8 @@
 
 # Standard procedures
 source $dir/Core.tcl
+
+# Eggdrop procedures
+proc strlen {text} {
+	string length $text
+}