A[n] [In]complete Character-Limiting Guide to Stack Exchange

Question

The Stack Exchange network user interface has a lot of forms, and subsequently, inputs with various character limits in place. Some of them are notorious (such as custom moderator flag character limit or the custom suggested edit reject reason one), some are less well-known.

It is past time we had a definitive guide on those for the sake of having documentation and for providing a unified place for tracking changes to the limits (should such a thing occur in 6 to 8 time units), so the question is:

What are the various character limits across the Stack Exchange network?

The scope of this Q&A is limited to character limits only.
For a detailed guide on rate-limiting, see the The Complete Rate-Limiting Guide.

Answer 1

Area 51

Input Field	Min	Max	Notes/Images
Example question	15	150	Min:
Proposal topic	3	150	Min:
Proposal audience	15	250	Min:
Proposal champions	15	500	Min:

Bounties

Input Field	Min	Max	Notes/Images
Bounty remarks (total characters)	30	3000	Min: Max: Reduce Character Limit for Bounty Custom Text
Bounty remarks (paragraphs/lines)	1	4	Max: Line breaks/paragraphs for bounty text

Close votes

Input Field	Min	Max	Notes/Images
"Other - add a comment" off-topic reason	30	500	Min:

Close reasons (Mod-only edits)

Input Field	Min	Max	Notes
Brief Description	10	100	e.g. "No longer reproducible"
Usage guidance, Close description, Post owner guidance, Privileged user guidance	25	500	See screenshot

Chat

Input Field	Min	Max	Notes
Single-line message	1	500	Max: What is the maximum length of a chat room message?
Chat search	0	80
Room description	0	500	Max: Chat room info/description max length

Contact Us

Input Field	Min	Max	Notes
Problem description	15	5000	Min:
Help center search	0	300

Edits

Input Field	Min	Max	Notes
Edit summary	depends	300	Minimum is 10 if suggesting an edit or you're a moderator editing an existing edit summary. There is no minimum for binding edits or when suggesting an edit to a tag wiki when you have enough reputation to review others' suggestions but not enough to make binding edits. On Stack Overflow in Japanese, the minimum is 5 instead of 10.
Suggested edits	6	depends	There is no max length limit for registered users, other than the post length limit. For anonymous users, there's an undisclosed limit, and hitting it will ban the IP address for 7 days. Sources: How do suggested edits work? How to overcome "Edits must be at least 6 characters"
Redaction explanation	1	300

Elections

Input Field	Min	Max	Notes
Nomination		1200	Max: Does anyone else think the moderator nominations are TLDR?
Questionnaire		12000	This is where candidates answer the questions.

Flags

Input Field	Min	Max	Notes/Images
"In need of moderator intervention" flag reason	10	500	Min:
"Something else" comment flag reason	6	200	Min: Max: For both post and comment flags, increase the maximum length permitted for the text of custom flags
Declined flag custom reason	10*	200	Min:
Helpful flag reason	10*	200	Min:

* The minimum length is only checked client-side and is not enforced server-side.

Help Center (Mod-only edits)

Input Field	Min	Max	Notes
Blurb under the favicon, Tour	???	???
"Ask about.." and "Don't ask about...", Tour	???	???
What topics can I ask about here?	???	???
Area under the search bar, Help Center	0	???

Posts

Input Field	Min	Max	Notes
Answers	30	30,0002	Max: Please increase the maximum allowed length for answers
Community Wikis	301	30,0002	Max: Character limit for wiki answers
Comments	151	600	Min: Why was the minimum comment length of 15 chosen?
Question body	301	30,0002	Min: Do some Stack Exchange sites have longer minimum question lengths than others? Max: Is there a limit on the length of a question?
Question title	151	150	Min: Able to break the minimum title length restriction?
Eligibility for tour page		4003	Maximum length for being eligible to appear on a site's tour page. Applies to the question and at least two of its answers, each. Unlike other character limits, this checks the rendered HTML of each post, not the Markdown. See: What determines the questions available for selection in the tour page?

¹ On Stack Overflow in Japanese and its per-site meta, the minimum requirement for question bodies is 20 characters, and the minimum requirement for comment bodies and question titles is 8 characters. This applies regardless of community wiki status. Answers are subject to the network default of 30.

² On Code Review, the character limit is 65,536 for all posts; see this comment. On Meta Stack Exchange, the limit is 50,000.

³ On Skeptics, there is no limit.

Profile

Input Field	Min	Max	Notes
About me	0	3000	Max: Could we get "n characters left" status when editing "About Me" in our profile?
Display Name	3	30	Min: Prevent (or at least notify about) display names shorter than 3 chars
Full Name	0	100
Location	0	100
Moderator annotatons	10	300

Reviews

Input Field	Min	Max	Notes
Suggested edit rejection reason	20	400	Min: Max: Increase the character limit of the custom edit rejection reasons

Search & Filters

Input Field	Min	Max	Notes
Site search	0	240	Max: Remove the max length restriction on the search boxes
Tag search	0	depends	Registered users may search for an unlimited number of tags. Anonymous users are restricted to searching for 3 tags at a time: the 4th and later tags are stripped out of the query; this applies even if wildcard tag syntax is being used, in which case it will be fully expanded to all matching tags and all except the first three will then be stripped out.
Tag filter	0	35

Tags

Input Field	Min	Max	Notes
Tag names	1	35	Max: Raising the 25 chars limit for tags
Tag excerpts	20	460	Min: Max: The Tag Wiki dropdown should display the entire tag wiki excerpt mentions 450, but the data-max-length on the input is actually set to 460
Tag wikis	30	unknown — at least 44,000 characters	Min: When editing from the revision history page (e.g., to edit from an old revision): the post length limit applies