Wikipedia:Edit filter/Traps and pitfalls
user alone throttles by user id, not username. All logged out editors share one user id,
0. This may cause false positives if multiple unrelated anonymous users match the filter conditions. If this is a problem, throttle by
ip instead.[note 2]
ip alone throttles logged in editors by their underlying IP address. Do not do this, unless the filter only targets logged out users. Instead, throttle by
ip, as above.
user_rights variable only contains the user's current rights. If the user has logged in using a bot password, or is editing with an OAuth application,
user_rights may be limited. For example, it looks like we could exclude extended confirmed users, bots, and administrators with[note 3]
!("extendedconfirmed" in user_rights) /* WRONG! */
but this will not work as expected if the user did not grant
editprotected when setting up a bot password. Instead, just specify the groups explicitly:
!contains_any(user_groups, "extendedconfirmed", "sysop", "bot")
Test/examine interface and recent changes
Some variables at Special:Abusefilter/test and Special:AbuseFilter/examine[note 4] will have different values from what they would have been, had the filter actually tripped at the time of the change.[note 5]
Suppose that Alice has a one hour old account, and adds the string "Hello, world! ~~~~" to a page that has only ever been edited by Bob.
|Variable||At save||At /examine or /test|
|added_lines||Hello, world! ~~~~||Hello, world! [[User:Alice|Alice]] ([[User talk:Alice|talk]]) 21:07, 14 November 2019 (UTC)[note 7]|
Order of operations
rlike and other keywords have a higher precedence than
+. This does not check if
added_lines contains "foo" or "bar":
added_lines rlike "foo" + "|bar" /* WRONG! */
added_lines rlike ("foo" + "|bar")
norm() and repeating characters
The norm() function strips out confusing (spoofed) characters, repeating characters, special characters, and whitespace. However it does this in a specific order (the order just mentioned). This can lead to unexpected results:
string := "A AB,BCC"; norm(string) == "ABC" /* FALSE */ norm(string) == "AABBC" /* TRUE */
If in doubt always use the debugging tool.
Creating a tag
Tags are created automatically when a filter is saved. Do not use the interface at the top of Special:Tags, unless you also want to activate the tag for manual use. Mistakenly activated tags may be deactivated from Special:Tags.
Be careful with arrays
The only operation that really works with arrays is
length. Other operations will implicitly cast an array to a string first. This could give an unintuitive result. For example,
page_namespace in [12, 34] is in fact equivalent to
string(page_namespace) in "12\n34\n". Therefore, when
page_namespace is 1, 2, 3, or 4, the expression will be evaluated to true as well. In the above case, use
equals_to_any(page_namespace, 12, 34) as a workaround instead.
Be careful with division
One might expect that
page_namespace / 2 === 0 will check if
page_namespace is either 0 or 1. However, the division operation in fact doesn't discard the remainder. That means, if the numerator is not divisible by the denominator, the result will be a float. In the above case, use
equals_to_any(page_namespace, 0, 1) instead.
Numeric comparisons with null
Like in PHP,
null is smaller than any number, i.e.
null < -1234567 is true. This is especially problematic when using
edit_delta: if the action being filtered is not an edit,
edit_delta < -5000 will evaluate to true. Remember to check that
action === "edit" when using
edit_delta like that.
- The title was shamelessly stolen from C Traps and Pitfalls.
- Not by
- All these groups have
extendedconfirmedrights, according to Special:UserGroupRights
- When examining recent changes. Examining old filter hits will show the correct values.
- See also T102944
- Not a filter log entry, if any exists
- This is actually the value of