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I noticed that I can only perform certain actions such as commenting a finite number of times in a given period of time. Obviously, rate limiting is in place to prevent accidental misuse or intentional abuse of certain features.

Where else is rate limiting applied on Stack Exchange sites, and what are the limits?

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295

Rate Limit Rationale

Loading pages

  • Undisclosed limit, applies to IP addresses
    • Applies to the entire network; if one makes too many requests on one or more sites, access to all network sites is restricted
    • Does not apply to non-load-balanced services not served from the same network as public Q&A (chat, the API, etc.)
    • Should not be triggered during normal browsing; if you get it, it either means you're sharing your IP with multiple users accessing the network, or your browser or an extension is hitting the site with one or more extra requests every time you load a page

Too many requests: This IP address has performed an unusual high number of requests and has been temporarily rate limited.

Comments

  • Voting & Flagging

    • Same amount of comment flags as one does post flags (default 10, may rise up to 100 based on flagging activity or reputation; see Flagging below)

      • Comment flag and post flag allowances are separate
    • 30 comment upvotes per day (automatic upvotes resulting from close votes do not count)

    • no minimum wait time between votes

      Comment voting - Daily vote limit reached; vote again in 3 hours

    • Can only flag one comment every 5 seconds

  • Deleting (treated like voting)

    • No limit per second (previous one-comment-per-5-second limit removed)
    • Can only delete own upvoted comments under 20 posts per day (multiple comments under same post are treated as one) You have already deleted your own comments from 20 posts today; further deletes are blocked
  • Creating

    Comment creation - You may add another comment in 24 seconds

  • Editing

    • comment can be edited every 5 seconds by its author or a diamond mod Comment editing - You may only edit a comment every 5 seconds
    • comments cannot be edited after 5 minutes (except by diamond moderators)

Searching

Asking

  • Users with < 125 rep on the current site, 40 minutes since their last question anywhere on the network (This applies to the user's IP address, not their account. If the user shares that IP with other users, they can be limited by the other user asking a question anywhere on the network; similarly, if the same user posts a question from a different IP address, they may not be limited.)

    Question limit - You can only post once every 40 minutes

    • Other per-site limits may apply; e.g. on Stack Overflow, new users can only ask once every 90 minutes. Some of these per-site limits do also check the account, not just the IP address.
    • While the limit is waived for users with 125+ reputation on a given site, questions posted on sites where one has 125+ reputation still count toward the rate limit for sites where one doesn't. For instance, if you ask a question on a site where you have 150 rep, you can't ask another question on a site where you have only 100 rep for the next 40 minutes; however, you can ask them in reverse order immediately (first on the 100-rep site, then on the 150-rep site).
  • Users limited by Anti-Recidivism System, one question per week

  • Users limited from asking questions for 1 – 7 days based on the performance of their previous questions

  • Users prevented from asking questions due to the quality filter: one question per 6 months

  • Users with < 10k rep trip CAPTCHA* if more than once per 60 seconds, or within 5 seconds of starting new post

  • Users with ≥ 10k rep trip CAPTCHA* if more than once per 30 seconds, or within 5 seconds of starting new post

  • On Stack Overflow, Super User, Server Fault and Mathematics (not active on all other sites)

    Sorry, you are only allowed to ask 50 questions in a 30 day period

  • Stack Exchange staff members are not subject to these rate limits on meta sites

Answering

  • Users with < 125 rep must wait 3 minutes between answers

  • Users with between 125 and 10k rep trip CAPTCHA* if more than once per 60 seconds, or within 5 seconds of starting new post

  • Users with ≥ 10k rep trip CAPTCHA* if more than once per 30 seconds, or within 5 seconds of starting new post

  • Users of any reputation level can only answer the same question once every 60 seconds

  • Users with the "staff" bit (i.e. Stack Exchange employees) are not subject to the above limits on meta sites

  • Maximum of 30000 characters for the Markdown source of answer.

    Answer Character Limit

Accepting

Editing

  • edit at most 5 of one's own posts per day, more for high-rep users (scales with reputation), does not apply to ♦ mods (multiple edits of same post are fine)

    You have already edited 5 of your own posts today; further edits are not allowed until tomorrow

  • At most 5 pending suggested edits per editor (20 on beta sites)

    • Limit is partially waived if submitting a tag wiki and excerpt suggested edit at the same time (which counts as two edits) - if the user only has space for one more pending edit, both edits will still be allowed, but they cannot submit another suggested edit until two of their pending edits are approved (i.e. they're no longer exceeding the limit)
  • Unregistered users can't suggest edits on posts < 10 minutes old

  • Users with < 10k rep trip CAPTCHA* if more than once per 30 seconds, or faster than 5 seconds after starting edit

  • Users with ≥ 10k rep trip CAPTCHA* if more than once per 10 seconds, or faster than 5 seconds after starting edit

  • You can only save a tag wiki edit once every 30 seconds, or once every 10 seconds if you have enough reputation (20k/4k on beta sites) to bypass the review queue. (Submitting a tag wiki edit along with a tag wiki excerpt edit at the same time for the same tag is not limited.)

* For all of the above thresholds for hitting CAPTCHA, if you have at least 200 reputation and have solved a CAPTCHA in the last 5 minutes, you will not have to solve one again.

Flagging

  • 10 flags per day by default

    • 1 bonus daily flag for every 10 net helpful flags in the user's flagging history (helpful minus declined, excluding other types such as disputed and aged away)
    • 1 bonus daily flag for every 2,000 reputation earned
    • A net negative helpful flag count can reduce a user's daily flag allowance to below 10
    • The number of daily flags is hard-capped at 100
  • 5 seconds between flags

  • 3 seconds between opening the flag dialog

    Flags per day

    Flag Rate Popup

    Flag Dialog Popup

  • You can be banned from flagging when too many flags have been declined in a 7 day period; such a ban will automatically be lifted once the criteria no longer apply (after at most 7 days).

Reviewing

Thank you for reviewing 20 Close Votes today; come back tomorrow to continue reviewing.

Chat

  • 1 second between two messages, here's the true throttle curve

Chat Throttle Curve

  • There is a similar throttle for starring (details unknown)
  • There is a similar throttle for searching (details unknown)
  • Star limit is 20 stars per room, per day for each user.
  • 30 seconds between creating chat bookmarks

Voting

  • 30 votes per day +10 for questions only (question-only votes can't be used once you've cast 25 votes on answers) (source)
    • To further elaborate: you get 10 Q-votes and 30 QA-votes per day. When you vote on a question, you'll use a Q-vote, and on an answer, you'll use a QA-vote. If you run out of Q-votes, you can continue voting on questions, but you'll be using QA-votes. However, once you have only 5 QA-votes left, you'll be blocked from using your Q-votes and all of your remaining voting for the day will use your QA-votes.
  • If one of the posts you vote on gets deleted the same day as you vote, your limit is recalculated as if you never cast that vote (i.e. in most cases, you can cast one more vote, but if you now have more than 5 unused QA-votes, your Q-votes will be unblocked, allowing you to vote more times).
  • If you vote and undo your vote 30 times, your vote gets locked in.

Your vote is now locked in

Logging in

  • 3 failed attempts within a minute before a CAPTCHA is displayed

Changing usernames

  • Last username change must be less than 15 minutes or more than 30 days ago. Does not apply to ♦ mods or accounts that are less than 2 days old.

Showing Upvote/Downvote totals

enter image description here

Expanding revision history from user activity

  • once per second

    You may only load 1 revision every second

Closing

  • Can open close dialog once per 3 seconds
  • 50 close/reopen votes/day/user on Stack Overflow, Mathematics, Server Fault, Super User and Ask Ubuntu, 12 on Stack Apps, 24 on others. Source

Close Dialog rate limit box

Deleting

  • Can only delete 5 of your own posts per day
  • 5 delete votes (at 10k) with an extra delete vote for every 1k rep above 10k, max of 30, per day
    • When a 10k+ user with delete votes remaining deletes one of their own posts, that deletion will deduct 1 from their delete votes for the day.
    • Other than that, the counts between self-deleted posts and delete votes for others' posts are kept separate: the number of self-deleted posts is hard-limited to 5, and if you've used all your delete votes but have deleted fewer than five of your own posts, you can still delete your own posts up to 5.
  • Question must be closed in order to be able to vote to delete it
  • A question can't be voted to delete until 2 days after closure, unless 20k+ and question score -3 or lower

Destroying accounts

  • Moderators can destroy only one account every 5 seconds.

Winter Bash hats

  • Change hat once every 10 seconds

iOS and Android apps

Stack Exchange API

  • Maximum of 300 queries per day per IP address, if not using a dedicated API key

  • Maximum of 10,000 queries per day per key and IP address pair, if using a dedicated API key, with some exceptions:

    • Some high-profile tools that actively help out with the Stack Exchange network receive special keys that grant them an extended limit (e.g. SmokeDetector has a limit of 20,000)
    • The above noted exemption for the mobile apps, which have special keys that don't have daily API limits (see above section for more details)
  • Maximum of one action-performing query per second

  • Occasionally, queries can return a backoff value, to indicate how much time a given application needs to wait before it can perform another query. This value depends on the number and speed of the queries and can change based on various other factors, and as such it's too complicated to fully list here.

  • 2
    How are rate limits for non-humans implemented? Is a count of searches within a short period of time (lets say 5 seconds) calculated each time someone does a search? – user784637 Feb 19 '13 at 8:41
  • 17
    Why are there even limits on the diamond mods? – Undo May 31 '13 at 15:52
  • @LanceRoberts What does "timer resets" mean, Sir? – Ave Maleficum Mar 9 '14 at 13:08
  • 2
    @AveMaleficum, when you vote on a comment, a timer starts. Everytime you click on the vote or flag button instead of having a smaller amount of time left, the timer resets itself. So you end up trying to time things in your head waiting for it to expire, see here. – Lance Roberts Mar 9 '14 at 16:00
  • 1
    There's also a limit for page requests per IP address per time period which I think must have recently been tightened (saw it twice yesterday) but I don't know what the exact limit is. – Martin Smith Mar 9 '14 at 17:44
  • Shouldn't per IP throttling occur only for anonymous users? IMO all API calls within the page should have a token associated with them and be throttled per user. – paulkon Mar 20 '14 at 17:21
  • What is the point of throttling per action with respect to DoS as opposed to global rate-limiting? – paulkon Mar 20 '14 at 17:36
  • 6
    ...yay, another 1 secondS. Why is it so hard to not fix all of these once and for all? – Werner Mar 30 '14 at 14:08
  • @Werner You linked to the tweet that answers your question. – michaelb958--GoFundMonica Mar 30 '14 at 21:07
  • 2
    @michaelb958: Sadly it doesn't answer it. It just gives Jeff's opinion about these things. There are so many quantifiers on this website and I wonder why nobody ever takes to time to consider the singular/plural issue from the start... It seems as simple as writing a function where you pass it the quantity and it will return either an "s" or nothing and append that to the quantifier. It seems so fundamentally straight-forward. – Werner Mar 31 '14 at 0:58
  • 2
    @Werner Jeff was the original CTO, and the pluralisation code was written under his watch (if not by him), so his opinion carries a little more weight. The current team could fix them now if it justified the resources, and if they weren't scared of the giant S. (They might be fixing them right now, and they just haven't told us yet so Jeff doesn't find out until that security upgrade's done.) – michaelb958--GoFundMonica Mar 31 '14 at 1:10
  • 3
    @LanceRoberts How should the chat throttle chart be interpreted? What's the data used to generate it? – Stijn Jul 28 '14 at 9:27
  • @Shadow, any reference on the comment rate-limit changes? – Lance Roberts Mar 11 '15 at 14:24
  • @Lance trial and error following this bug report - asked the dev for confirmation. – Shadow Wizard Wearing Mask Mar 11 '15 at 15:01
  • @Werner, perhaps they should use MediaWiki's jquery.i18n. – Nemo Apr 29 '15 at 9:17

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