As a rule of thumb, when in doubt, do not block; instead, consult other administrators for advice. After placing a block that may be controversial, it is a good idea to make a note of the block at the administrators' noticeboard for peer review. Range blocks are especially powerful tools and discussion of these is particularly encouraged.
Blocks may be applied for a number of reasons. The more common of these are detailed below:
- Vandalism. Disruptive editing or uploading may result in a block. For example:
- Insertion of gratuitous vulgarity
- Insertion of deliberately false information (e.g. fake image sources)
- Edit warring.
- Copyright violations. Repeated uploading of inappropriately licensed media is grounds for blocking an account. Clear explanations and warnings about Commons policy should be engaged in before and after blocking a user for license problems.* Harassment. Accounts and IP addresses which are used primarily to create a hostile environment for another user may be blocked. Good faith disputes between users, however, should be brought to Commons:Village pump for outside input. Tracking a user's contributions for policy violations is not harassment.
- Unauthorized or non-responsive bot accounts. Bot accounts not authorized by the Commons community are not allowed to operate on Wikimedia Commons, and questionable bot-like editing that cannot be explained by the user should be blocked until discussion takes place. Bot proposals can be discussed at Commons:Bots or Commons:Village pump. Bots may not be operated on Commons without advance permission (which can be sought at Commons:Bots/Requests).
- Approved bot accounts that are temporarily malfunctioning. This to prevent additional damage until the bot-owner can address the problem.
- Inappropriate usernames.* Evasion of blocks. An administrator may reset the block of a user who intentionally evades a block, and may extend the duration of the block if the user engages in further blockable behaviour while evading the block. User accounts or IP addresses used to evade a block may and should also be blocked.
- Abusing multiple accounts to mislead, deceive, disrupt, distort consensus or to evade blocks or other sanctions. Secondary accounts are typically blocked indefinitely. The primary account may or may not be subject to new or extended blocks depending on the circumstances.
- Open or anonymizing proxies are typically blocked upon detection in accordance with Wikimedia-wide policy. The normal duration of such blocks is one year.
- For blocks based on disruptive behavior, such as vandalism, repeated copyright violations and manual promotional activities, ensure that the user has been appropriately warned, preferably using a block warning template. No warning is necessary when blocking open proxies and users with inappropriate usernames. Accounts and IP addresses used solely for severely disruptive purposes such as automated spamming, serious vandalism or harassment may also be blocked without prior warning.
- Controversial blocks may be discussed at the blocks and protections noticeboard, preferably before they are applied if at all possible. As a rule of thumb, when in doubt, do not block.
- Range blocks are especially powerful tools, and discussion of these is particularly encouraged. Range blocks with a duration longer than 24 hours should be discussed with a checkuser to assess the likely impact.
- Blocks can be applied to registered users, IP addresses or address ranges.
- As blocks are preventative rather than punitive, use a block duration that is proportional to the time likely needed for the user to familiarize themselves with relevant policies and adjust their behavior. Also consider the user's past behavior and the severity of the disruption. When blocking IP addresses, keep in mind that innocent third parties sharing the same addresses may be affected.
- Provide a reason for the block. The rationale should preferably use links to relevant policies to help the blocked user understand why they have been blocked. Where appropriate, diffs or permanent links documenting the reason for the block are also helpful.
- Account creation should be prevented in most cases, but may be allowed when blocking an inappropriate user name to allow creation of a different name.
- Autoblocking of IP addresses used by the blocked user should typically be disabled when blocking bots and enabled in most other cases.
- Only prevent the blocked user from using their talk page or sending e-mail if they are likely to abuse these privileges.
- Notify the blocked user, preferably using a user block template.
- Watch the blocked user's user talk page and ensure that requests for unblock are attended to.
- Blocks based on disruptive behavior should be lifted if there is reason to believe that the disruptive behavior will not resume.
- Controversial blocks may also be discussed at the blocks and protections noticeboard after they have been applied. To avoid wheel warring, they should only be lifted by another administrator if there is consensus to do so, even if there is no clear consensus in favor of the original block.