<s>
WebSub	B-Application
(	O
formerly	O
PubSubHubbub	B-Application
)	O
is	O
an	O
open	O
protocol	O
for	O
distributed	O
publish	B-Operating_System
–	I-Operating_System
subscribe	I-Operating_System
communication	O
on	O
the	O
Internet	O
.	O
</s>
<s>
Initially	O
designed	O
to	O
extend	O
the	O
Atom	B-Application
(	O
and	O
RSS	O
)	O
protocols	O
for	O
data	O
feeds	O
,	O
the	O
protocol	O
can	O
be	O
applied	O
to	O
any	O
data	O
type	O
(	O
e.g.	O
</s>
<s>
HTML	B-Language
,	O
text	O
,	O
pictures	O
,	O
audio	O
,	O
video	O
)	O
as	O
long	O
as	O
it	O
is	O
accessible	O
via	O
HTTP	O
.	O
</s>
<s>
Its	O
main	O
purpose	O
is	O
to	O
provide	O
real-time	O
notifications	B-Application
of	O
changes	O
,	O
which	O
improves	O
upon	O
the	O
typical	O
situation	O
where	O
a	O
client	O
periodically	O
polls	B-General_Concept
the	O
feed	O
server	O
at	O
some	O
arbitrary	O
interval	O
.	O
</s>
<s>
In	O
this	O
way	O
,	O
WebSub	B-Application
provides	O
pushed	O
HTTP	O
notifications	B-Application
without	O
requiring	O
clients	O
to	O
spend	O
resources	O
on	O
polling	B-General_Concept
for	O
changes	O
.	O
</s>
<s>
In	O
October	O
2017	O
,	O
PubSubHubbub	B-Application
was	O
renamed	O
to	O
WebSub	B-Application
for	O
simplicity	O
and	O
clarity	O
.	O
</s>
<s>
,	O
the	O
WebSub	B-Application
protocol	O
has	O
been	O
adopted	O
by	O
the	O
W3C	O
as	O
a	O
Recommendation	O
.	O
</s>
<s>
Under	O
WebSub	B-Application
,	O
there	O
is	O
an	O
ecosystem	O
of	O
publishers	O
,	O
subscribers	O
,	O
and	O
hubs	O
.	O
</s>
<s>
The	O
subscriber	O
needs	O
to	O
run	O
a	O
web	O
accessible	O
server	O
so	O
that	O
hubs	O
can	O
directly	O
notify	O
it	O
when	O
any	O
of	O
its	O
subscribed	O
topics	O
have	O
updated	O
,	O
using	O
a	O
webhook	B-Protocol
mechanism	O
.	O
</s>
<s>
They	O
post	O
notifications	B-Application
to	O
those	O
referenced	O
hubs	O
whenever	O
they	O
publish	O
something	O
.	O
</s>
<s>
WebSub	B-Application
includes	O
a	O
simple	O
verification	O
of	O
intent	O
mechanism	O
in	O
order	O
to	O
prevent	O
abusive	O
subscriptions	O
,	O
and	O
a	O
validation	O
mechanism	O
allows	O
for	O
subscriptions	O
to	O
private	O
or	O
protected	O
web	O
resources	O
.	O
</s>
<s>
In	O
order	O
to	O
provide	O
a	O
secure	O
chain	O
,	O
subscribers	O
should	O
share	O
a	O
secret	O
with	O
the	O
hub	O
,	O
which	O
will	O
be	O
used	O
by	O
the	O
hub	O
to	O
compute	O
an	O
HMAC	B-Algorithm
key	O
that	O
will	O
be	O
sent	O
to	O
the	O
subscriber	O
.	O
</s>
<s>
WebSub	B-Application
is	O
used	O
to	O
push	O
content	O
by	O
many	O
websites	O
,	O
including	O
all	O
blogs	O
served	O
by	O
Blogger	B-Application
and	O
WordPress.com,	O
news	O
sites	O
including	O
CNN	B-Architecture
and	O
Fox	O
News	O
,	O
and	O
social	O
networks	O
like	O
diaspora*	O
,	O
Mastodon	B-Application
,	O
MySpace	B-Application
or	O
Medium.com	B-Protocol
.	O
</s>
<s>
Subscribing	O
services	O
(	O
“	O
feed	O
readers	O
”	O
)	O
include	O
Flipboard	B-Application
,	O
Feedly	B-Application
,	O
NewsBlur	B-Application
,	O
among	O
other	O
popular	O
options	O
.	O
</s>
<s>
Community	O
Hosted	O
hub	O
providers	O
include	O
pubsubhubbub.appspot.com	O
(	O
operated	O
by	O
Google	B-Application
)	O
,	O
pubsubhubbub.superfeedr.com	O
(	O
operated	O
by	O
Superfeedr	B-Application
)	O
,	O
and	O
websubhub.com	O
.	O
</s>
<s>
Superfeedr	B-Application
provides	O
a	O
detailed	O
PubSubHubbub	B-Application
guide	O
for	O
implementation	O
.	O
</s>
