Every web developer should know how to properly code a responsive website. Bootstrap 3 is an ultimate framework that learns you how to think when coding responsive websites and makes their creation much easier and faster. When I was learning Bootstrap 3, I was looking for a simple list of basic Bootstrap 3 classes with description and there were none - only a few lists for Bootstrap 2, without any description, therefore pretty useless for my intentions. So I created this list of Bootstrap 3 CSS classes with so much desired description - I hope it's comprehensive. Keep in mind that it's not a documentation, it's just a quick hint to help you understand the meaning of each mentioned class.

It is also not a complete list of classes, it would take days to create it and you don't really need to use (and know) all the BS3 classes. See the sources part in the bottom of this page to find out the meaning of the classes that I don't mention here (button classes for example).

Basic Bootstrap Classes
.container

sets fixed width to an element (which changes depending on a screen size to other fixed values, so it's still responsive) on all screen sizes except xs - on xs, the width is calculated automatically (this behaviour can be changed)
a fixed width responsive website should be wrapped in .container (or just the content without menu, whatever - it's up to you)
.container can't be nested!
.container-fluid

sets 100% width, margin-left and margin-right: auto, padding-left and padding-right: 15px
a full screen website should be wrapped in .container-fluid
.container-fluid can't be nested!
.row

creates horizontal groups of columns (which usually have width classes, see below)
must be within .container to ensure correct padding and alignment
only columns (block elements with width classes) may be immediate children of rows
sets margin-left and margin-right: -15px
.pull-right

.pull-left

sets float to either left or right
.center-block

sets margin-left and margin-right to auto
Bootstrap Grid Classes
can be nested, the nested columns must be wrapped in .row as well
all columns have float: left and position: relative styles
.col-xs-1

.col-xs-2

.col-xs-3

.col-xs-4

.col-xs-5

.col-xs-6

.col-xs-7

.col-xs-8

.col-xs-9

.col-xs-10

.col-xs-11

.col-xs-12

sets width of a column (specified in %) on extra small screens (<768pxt)
.col-sm-1

.col-sm-2

.col-sm-3

.col-sm-4

.col-sm-5

.col-sm-6

.col-sm-7

.col-sm-8

.col-sm-9

.col-sm-10

.col-sm-11

.col-sm-12

sets width of a column (specified in %) on small screens (≥768px)
.col-md-1

.col-md-2

.col-md-3

.col-md-4

.col-md-5

.col-md-6

.col-md-7

.col-md-8

.col-md-9

.col-md-10

.col-md-11

.col-md-12

sets width of a column (specified in %) on medium size screens (≥992px)
.col-lg-1

.col-lg-2

.col-lg-3

.col-lg-4

.col-lg-5

.col-lg-6

.col-lg-7

.col-lg-8

.col-lg-9

.col-lg-10

.col-lg-11

.col-lg-12

sets width of a column (specified in %) on large screens (≥1200px)
.col-xs-offset-* (.col-xs-offset-1, .col-xs-offset-2, .col-xs-offset-3 ... up to -12)

.col-sm-offset-* (.col-sm-offset-1, .col-sm-offset-2, .col-sm-offset-3 ... up to -12)

.col-md-offset-* (.col-md-offset-1, .col-md-offset-2, .col-md-offset-3 ... up to -12)

.col-lg-offset-* (.col-lg-offset-1, .col-lg-offset-2, .col-lg-offset-3 ... up to -12)

sets offset (margin-left) by specified number of columns (eg. set .col-sm-offset-3 class to a column to move it by three columns on small screens)
.col-xs-pull-* (.col-xs-pull-1, .col-xs-pull-2 ... up to -12)

.col-sm-pull-* (.col-sm-pull-1, .col-sm-pull-2 ... up to -12)

.col-md-pull-* (.col-md-pull-1, .col-md-pull-2 ... up to -12)

.col-lg-pull-* (.col-lg-pull-1, .col-lg-pull-2 ... up to -12)

sets left position in % as it is with columns (e.g. left: 75% with -pull-9)
.col-xs-push-* (.col-xs-push-1, .col-xs-push-2 ... up to -12)

.col-sm-push-* (.col-sm-push-1, .col-sm-push-2 ... up to -12)

.col-md-push-* (.col-md-push-1, .col-md-push-2 ... up to -12)

.col-lg-push-* (.col-lg-push-1, .col-lg-push-2 ... up to -12)

sets right position in % as it is with columns (e.g. right: 25% with -push-3)
Bootstrap Visibility Classes
you can apply all as many of these classes on a single element as you wish and this mixing gives you even more possibilities for your layout
.clearfix

obvious, clear: both
often combined with classes below
.visible-xs-block and .visible-xs

.visible-sm-block and .visible-sm

.visible-md-block and .visible-md

.visible-lg-block and .visible-lg

displays element (sets display: block property) only on screens with specified size and hides it (sets display: none) on screens of other sizes automatically
often combined with .clearfix so that clearfix is effective only on the selected screen size
.visible-xs-inline-block

.visible-sm-inline-block

.visible-md-inline-block



.visible-lg-inline-block

displays element (sets display: inline-block property) only on screens with specified size and hides it (sets display: none) on screens of other sizes automatically
.visible-xs-inline

.visible-sm-inline

.visible-md-inline

.visible-lg-inline

displays element (sets display: block property) only on screens with specified size and hides it (sets display: none) on screens of other sizes automatically
.hidden-xs

.hidden-sm

.hidden-md

.hidden-lg

hides element (sets display: none property) only on screens with specified size and hides it (sets display: none) on screens of other sizes automatically
.visible-print-block

displays element (sets display: block) in print (pre)view
.visible-print-inline

displays element (sets display: inline) in print (pre)view
.visible-print-inline-block

displays element (sets display: inline-block) in print (pre)view
.hidden-print

hides element (sets display: none) in print (pre)view
Bootstrap Typography Classes
default font-size of <body> a <p> elements is 14px, line-height 1.428; <p> also has margin-bottom of half of its line-height (20px with 14px font), therefore 10px by default
all elements like b, big, code, em, i, mark, small, strong, sub, sup, ins, del, s, u, abbr, address and blockquote (and small and cite inside) are properly styled
vast majority of these classes are most often set to either paragraph, strong or em elements
.page-header

class for a wrapping div of a heading
adds some margin, padding and border-bottom
.h1

.h2

.h3

.h4

.h5

.h6

makes an element look like heading of a chosen level
.lead

for highlighting an element
sets element's font-size to 21px, font-weight: 300, line-height: 1.4 and margin-bottom: 20px
.text-left

.text-center

.text-right

.text-justify

aligns texts, usually paragraphs, with text-align CSS property
.text-nowrap

keeps the whole text with this class on a single line, no wrapping occurs because of white-space: nowrap CSS property of this class
.text-lowercase

.text-uppercase

.text-capitalize

sets text-transform CSS property to make all characters inside the element with this class lowercase, uppercase or capitalized
.text-muted

makes text grey
.text-primary

makes text blue
.text-success

makes text green
.text-info

makes text dark blue
.text-warning

makes text dark yellow
.text-danger

makes text red
Bootstrap Lists' Classes
.list-unstyled

removes list-style and margin-left on list items
doesn't apply for nested lists (if needed, the nested list has to have .list-unstyled class as well)
.list-inline

places list items on a single line (with display: inline-block and padding)
.dl-horizontal

class for a definition list (<dl>)
sets nice styles for <dt> and <dd> within the definition list (text align, font-weight)
.list-group

class for the parent element (usually <ul>, but can be <div> as well) of list items
list items have to have .list-group-item class
.list-group-item

class for .list-group children elements
for a nicer look of the list items
usually on <li>, but can be <a> as well
.list-group-item-heading

for a heading within .list-group-item, often <h4> or similar low-level heading
.list-group-item-text

for text within .list-group-item, often in the paragraph tag or just in a span
Bootstrap Tables' Classes
.table

for an ordinary table
table heading has only border-bottom and <td>s have only border-top
.table-striped

every odd line will be darker for a nicer look (using :nth-child selector)
table heading <th> has only border-bottom and <td>s have only border-top
should be combined with .table class
.table-bordered

table with borders all around
should be combined with .table class
.table-hover

class for a table
adds hover/focus effect on the table's tbody rows
should be combined with .table class
.table-condensed

should be combined with .table class
for an ordinary table with half cell padding, so rows are not that high
.table-responsive

class for a wrapper (! mostly div) of a table to keep it responsive in the way that scrollbar appears on extra small devices
.active

.success

.info

.warning

.danger

classes for either <tr> or just <td>
sets background color for all <td> in a table row (or just one <td>) to grey (active) / green (success) / blue (info) / yellow (warning) / red (danger)
Bootstrap Forms' Classes
don't forget that even form elements can be in the Bootstrap grid, so don't be afraid to use .row inside a form and then col-*-* wrappers
.form-group

when creating vertical forms, it's a class for its wrapper (mostly div) of each label and its input, adds some margin-bottom
.form-control

for every form element (input, textarea...), gives it 100% width
to make it narrower, use a narrower wrapper (row and col-*-* divs)
.form-control-static

for a paragraph that replaces a form element (input...)
.form-horizontal

for horizontal forms where label is on the same line as input
you have to use column classes (like col-xs-10) for each label and its input (or whateveer it is)
still combined with .form-group wrapper and .form-control classes
.form-inline

for a single line form (but still vertical on extra small screens)
often used with the placeholder attribute to not need labels
labels of inline forms should get .sr-only class to be positioned so that they can't be seen (but they won't get display: none or visibility: hidden property)
.input-lg

.input-sm

makes a form element like input or select either bigger or smaller than default
.input-group-lg

.input-group-sm

classes for .input-group (see further)
always used together with .input-group class
.input-group

class for a wrapper of .input-group-addon or .input-group-btn
used instead of form-group when the classes above are used
.input-group-addon

class for a span that serves as a wrapper for either .glyphicon or a radio/checkbox input
adds your choice (glyphicon...) on the inner edge of an input field with grey background
the span with this class can be either before or after input, depends where you want the icon to show (the left or right side of the input)
must be within .input-group
.input-group-btn

class for a span that serves as a wrapper for a button that looks like it was within a form input
the span with this class can be either before or after input, depends where you want the button to show (left or right side of the input)
contains <button> (the button can also include .dropdown-toggle class, span with .caret class and data-toggle="dropdown" attribute for even more complicated buttons)
must be within .input-group
.caret

class for an empty span that creates a dropdown arrow
.help-block

class for a span that serves as a help text for users
has to be placed right after an input of a form
.has-success

.has-warning

.has-error

classes for wrapping divs with .form-group class
colours the label, input and .help-block span inside to green/yellow/red
the label within the wrapper with one of these classes has to have .control-label class to be coloured as well
.has-feedback

class for the wrapping divs with .form-group class when you also use glyphicon for the input within the wrapper
To disable input, use disabled="disabled" or readonly="readonly",
To disable whole fieldset, wrap form-groups to fieldset with disabled="disabled"

Bootstrap Image Classes
images should have .img-responsive or .thumbnail to be responsive and be wrapped in a column wrapper (like col-xs-3...)
.img-rounded

img class that provides little border-radius
.img-circle

img class that provides 50% border-radius making the img circle shaped
.img-thumbnail

img class that provides a 1px solid grey border, 4px padding, white background, display: inline-block property and fast CSS3 transition
.thumbnail

class for a wrapping div (or <a> in case of gallery) of an image, adds some styles (border, padding, background, transition) and set's the image max-width: 100%, height: auto; display: block; and margin-left and margin-right: auto
.img-responsive

img class that makes any image responsive (scaling to the parent element) as it has max-width: 100% and height: auto
may not work if placed in a floating element!
.caption

class for a div inside .thumbnail element (a or div) that may include h3, p, a (also buttons) for a proper margin/padding
.media

class for a div (or li, whatever) that may contain an image, a heading, some <small> text and paragraphs
ensures proper image margin/padding
heading inside should also have media-heading attribute and should be (together with paragraphs) wrapped in a .media-body wrapper
any image within should have .pull-left or .pull-right class to float
.media-list

class for a list (ul, ol) that contains .media inside
ensures better margin/padding
.glyphicon

base class for glyphicons (font-based icons), sets font, its styles and positioning
should be used on a span
.glyphicon-* (replace the star with any name of a glyphicon from this list)

sets picture via font and :before CSS3 selector with content of the font
must be used together with .glyphicon class to show proper image
should be used on a span
Bootstrap Embed Classes
.embed-responsive

general class for responsive embedding wrapper
.embed-responsive-4by3

.embed-responsive-16by9

specific class for the embed wrapper with ratio already set
used together with .embed-responsive class
.embed-responsive-item

used on the iframe or whatever it is inside the wrapper
Bootstrap Navigation Classes
.nav

the basic class for every navigation structure (<ul>), removes any list-style, left padding and bottom margin
also sets display: block and position relative for its <li> children
must be set on every navigation
.active

class for a list item (nav item, li) that makes it look active / current
.nav-tabs

class for navigation structure that gives it a tab style (proper borders + float: left)
.nav-pills

class for navigation structure that gives it a pills style (background on active nav item)
.nav-stacked

makes vertical pills navigation
used together with .nav-pills (and .nav of course)
.dropdown

class for an
nav item to make it dropdown
needs additional classes elsewhere to work (see below)
.dropdown-toggle

class for an <a> which is within <li class="dropdown"> to make a dropdown menu
needs additional classes elsewhere to work (see below)
.dropdown-menu

class for an <ul> which is within <a class="dropdown-toggle"> to make a dropdown menu
provides proper displaying and hiding
the most important dropdown menu class
needs .dropdown and .dropdown-toggle classes on parent elements (see above)
.nav-justified

class for an <ul>, together with .nav-tabs or .nav-pills creates a navigation with centered text and links' parent elements of the same width
.disabled

class for <li> in a navigation
disables the link inside VISUALLY and also adds a special mouse cursor, but the link remains active - you need to remove the href attribute of the <a> to completely disable the link
Bootstrap Navbar Classes
the difference between nav and navbar classes is the fact that navbar can collapse the whole nav (the nav can't do it on its own)
.navbar

basic class for a navigation wrapper (usually <nav>), sets border, bottom margin, min-height and position: relative
if it's not supposed to be fixed, can be placed anywhere in .container or .container-fluid
.navbar-default

sets other basic styles for a navigation wrapper (background gradient and box-shadow) and also its items (including .active class on <li>s)
for dark colours, see .navbar-inverse below
.navbar-inverse

variation of navbar-default but with dark colours
never use navbar-default and navbar-inverse on one element as it doesn't make any sense
.navbar-brand

sets styles for special hyperlinks and other "simple text" in a menu (float: left, bigger font size, some padding, text-shadow...)
.navbar-fixed-top

.navbar-fixed-bottom

additional class to .navbar that makes the navigation fixed at the top (or bottom) of the page as you scroll
used together with .navbar and also .navbar default (just to keep the nice look)
you should add some top or bottom padding to your <body> to not let the navbar overflow your content
.navbar-static-top

removes top, right and left border and also border-radius of your navigation
.breadcrumb

class for <ul> that serves as breadcrumbs
gives breadcrumbs a cool look
.pagination

class for <ul> that serves as pagination
properly styles <li> within this pagination also with .disabled and .active classes (keep in mind that .disabled doesn't remove link's functionality)
.pagination-lg

.pagination-sm

used on <ul> together with .pagination, makes pagination either bigger or smaller than default
.pager

used on <ul>, styles "Previous" and "Next" links to look better with a grey border
its list items can have .previous, .next and also disabled classes for even better styling
.next

.previous

used on <li> within <ul class="pager">, adds arrows to the links