<s>
Googlebot	B-Application
is	O
the	O
web	B-Application
crawler	I-Application
software	O
used	O
by	O
Google	B-Application
that	O
collects	O
documents	O
from	O
the	O
web	O
to	O
build	O
a	O
searchable	O
index	O
for	O
the	B-Application
Google	I-Application
Search	O
engine	O
.	O
</s>
<s>
This	O
name	O
is	O
actually	O
used	O
to	O
refer	O
to	O
two	O
different	O
types	O
of	O
web	B-Application
crawlers	I-Application
:	O
a	O
desktop	O
crawler	O
(	O
to	O
simulate	O
desktop	O
users	O
)	O
and	O
a	O
mobile	O
crawler	O
(	O
to	O
simulate	O
a	O
mobile	O
user	O
)	O
.	O
</s>
<s>
A	O
website	O
will	O
probably	O
be	O
crawled	O
by	O
both	O
Googlebot	B-Application
Desktop	O
and	O
Googlebot	B-Application
Mobile	O
.	O
</s>
<s>
However	O
Google	B-Application
announced	O
that	O
,	O
starting	O
from	O
September	O
2020	O
,	O
all	O
sites	O
were	O
switched	O
to	O
mobile-first	O
indexing	O
,	O
meaning	O
Google	B-Application
is	O
crawling	O
the	O
web	O
using	O
a	O
smartphone	O
Googlebot	B-Application
.	O
</s>
<s>
The	O
subtype	O
of	O
Googlebot	B-Application
can	O
be	O
identified	O
by	O
looking	O
at	O
the	O
user	B-Protocol
agent	I-Protocol
string	O
in	O
the	O
request	O
.	O
</s>
<s>
However	O
,	O
both	O
crawler	O
types	O
obey	O
the	O
same	O
product	O
token	O
(	O
useent	O
token	O
)	O
in	O
robots.txt	O
,	O
and	O
so	O
a	O
developer	O
cannot	O
selectively	O
target	O
either	O
Googlebot	B-Application
mobile	O
or	O
Googlebot	B-Application
desktop	O
using	O
robots.txt	O
.	O
</s>
<s>
If	O
a	O
webmaster	O
chooses	O
to	O
restrict	O
the	O
information	O
on	O
their	O
site	O
available	O
to	O
a	O
Googlebot	B-Application
,	O
or	O
another	O
spider	B-Application
,	O
they	O
can	O
do	O
so	O
with	O
the	O
appropriate	O
directives	O
in	O
a	O
robots.txt	O
file	O
,	O
or	O
by	O
adding	O
the	O
meta	O
tag	O
<meta name="Googlebot" content="nofollow" />	O
to	O
the	O
web	O
page	O
.	O
</s>
<s>
Googlebot	B-Application
requests	O
to	O
Web	B-Application
servers	I-Application
are	O
identifiable	O
by	O
a	O
user-agent	B-Protocol
string	O
containing	O
"	O
Googlebot	B-Application
"	O
and	O
a	O
host	O
address	O
containing	O
"	O
googlebot.com	O
 "	O
.	O
</s>
<s>
Currently	O
,	O
Googlebot	B-Application
follows	O
HREF	O
links	O
and	O
SRC	O
links	O
.	O
</s>
<s>
There	O
is	O
increasing	O
evidence	O
Googlebot	B-Application
can	O
execute	O
JavaScript	O
and	O
parse	O
content	O
generated	O
by	O
Ajax	B-General_Concept
calls	O
as	O
well	O
.	O
</s>
<s>
There	O
are	O
many	O
theories	O
regarding	O
how	O
advanced	O
Googlebot	B-Application
's	O
ability	O
is	O
to	O
process	O
JavaScript	O
,	O
with	O
opinions	O
ranging	O
from	O
minimal	O
ability	O
derived	O
from	O
custom	O
interpreters	O
.	O
</s>
<s>
Currently	O
,	O
Googlebot	B-Application
uses	O
a	O
web	O
rendering	O
service	O
(	O
WRS	O
)	O
that	O
is	O
based	O
on	O
the	O
Chromium	B-Language
rendering	O
engine	O
(	O
version	O
74	O
as	O
on	O
7	O
May	O
2019	O
)	O
.	O
</s>
<s>
Googlebot	B-Application
discovers	O
pages	O
by	O
harvesting	O
every	O
link	O
on	O
every	O
page	O
that	O
it	O
can	O
find	O
.	O
</s>
<s>
Unless	O
prohibited	O
by	O
a	O
nofollow-tag	O
,	O
it	O
then	O
follows	O
these	O
links	O
to	O
other	O
web	O
pages	O
.	O
</s>
<s>
A	O
problem	O
that	O
webmasters	O
with	O
low-bandwidth	O
Web	O
hosting	O
plans	O
have	O
often	O
noted	O
with	O
the	O
Googlebot	B-Application
is	O
that	O
it	O
takes	O
up	O
an	O
enormous	O
amount	O
of	O
bandwidth	O
.	O
</s>
<s>
Google	B-Application
provides	O
"	O
Search	B-Application
Console	I-Application
"	O
that	O
allow	O
website	O
owners	O
to	O
throttle	O
the	O
crawl	O
rate	O
.	O
</s>
<s>
How	O
often	O
Googlebot	B-Application
will	O
crawl	O
a	O
site	O
depends	O
on	O
the	O
crawl	O
budget	O
.	O
</s>
<s>
Technically	O
,	O
Googlebot	B-Application
's	O
development	O
team	O
(	O
Crawling	O
and	O
Indexing	O
team	O
)	O
uses	O
several	O
defined	O
terms	O
internally	O
to	O
take	O
over	O
what	O
"	O
crawl	O
budget	O
"	O
stands	O
for	O
.	O
</s>
<s>
Since	O
May	O
2019	O
,	O
Googlebot	B-Application
uses	O
the	O
latest	O
Chromium	B-Language
rendering	O
engine	O
,	O
which	O
supports	O
ECMAScript	O
6	O
features	O
.	O
</s>
<s>
Mediabot	O
is	O
the	O
web	B-Application
crawler	I-Application
that	O
Google	B-Application
uses	O
for	O
analyzing	O
the	O
content	O
so	O
Google	B-Application
AdSense	O
can	O
serve	O
contextually	O
relevant	O
advertising	O
to	O
a	O
web	O
page	O
.	O
</s>
<s>
Mediabot	O
identifies	O
itself	O
with	O
the	O
user	B-Protocol
agent	I-Protocol
string	O
"	O
Mediapartners-Google/2.1	O
"	O
.	O
</s>
