<s>
Heritrix	B-Application
is	O
a	O
web	B-Application
crawler	I-Application
designed	O
for	O
web	O
archiving	O
.	O
</s>
<s>
It	O
is	O
available	O
under	O
a	O
free	B-License
software	I-License
license	I-License
and	O
written	O
in	O
Java	B-Language
.	O
</s>
<s>
The	O
main	O
interface	O
is	O
accessible	O
using	O
a	O
web	B-Application
browser	I-Application
,	O
and	O
there	O
is	O
a	O
command-line	B-Application
tool	I-Application
that	O
can	O
optionally	O
be	O
used	O
to	O
initiate	O
crawls	O
.	O
</s>
<s>
Heritrix	B-Application
was	O
developed	O
jointly	O
by	O
the	O
Internet	O
Archive	O
and	O
the	O
Nordic	O
national	O
libraries	O
on	O
specifications	O
written	O
in	O
early	O
2003	O
.	O
</s>
<s>
For	O
many	O
years	O
Heritrix	B-Application
was	O
not	O
the	O
main	O
crawler	O
used	O
to	O
crawl	O
content	O
for	O
the	O
Internet	O
Archive	O
's	O
web	O
collection	O
.	O
</s>
<s>
The	O
Internet	O
Archive	O
itself	O
did	O
some	O
of	O
its	O
own	O
crawling	O
using	O
Heritrix	B-Application
,	O
but	O
only	O
on	O
a	O
smaller	O
scale	O
.	O
</s>
<s>
A	O
number	O
of	O
organizations	O
and	O
national	O
libraries	O
are	O
using	O
Heritrix	B-Application
,	O
among	O
them	O
:	O
</s>
<s>
Older	O
versions	O
of	O
Heritrix	B-Application
by	O
default	O
stored	O
the	O
web	O
resources	O
it	O
crawls	O
in	O
an	O
Arc	B-Application
file	I-Application
.	O
</s>
<s>
This	O
file	O
format	O
is	O
wholly	O
unrelated	O
to	O
ARC	B-Application
(	O
file	O
format	O
)	O
.	O
</s>
<s>
This	O
format	O
has	O
been	O
used	O
by	O
the	O
Internet	O
Archive	O
since	O
1996	O
to	O
store	O
its	O
web	B-General_Concept
archives	I-General_Concept
.	O
</s>
<s>
More	O
recently	O
it	O
saves	O
by	O
default	O
in	O
the	O
WARC	B-General_Concept
file	I-General_Concept
format	I-General_Concept
,	O
which	O
is	O
similar	O
to	O
ARC	B-Application
but	O
more	O
precisely	O
specified	O
and	O
more	O
flexible	O
.	O
</s>
<s>
Heritrix	B-Application
can	O
also	O
be	O
configured	O
to	O
store	O
files	O
in	O
a	O
directory	O
format	O
similar	O
to	O
the	O
Wget	B-Protocol
crawler	O
that	O
uses	O
the	O
URL	O
to	O
name	O
the	O
directory	O
and	O
filename	O
of	O
each	O
resource	O
.	O
</s>
<s>
An	O
Arc	B-Application
file	I-Application
stores	O
multiple	O
archived	O
resources	O
in	O
a	O
single	O
file	O
in	O
order	O
to	O
avoid	O
managing	O
a	O
large	O
number	O
of	O
small	O
files	O
.	O
</s>
<s>
The	O
file	O
consists	O
of	O
a	O
sequence	O
of	O
URL	O
records	O
,	O
each	O
with	O
a	O
header	O
containing	O
metadata	O
about	O
how	O
the	O
resource	O
was	O
requested	O
followed	O
by	O
the	O
HTTP	B-Protocol
header	I-Protocol
and	O
the	O
response	O
.	O
</s>
<s>
Arc	B-Application
files	I-Application
range	O
between	O
100	O
and	O
600	O
MB	O
.	O
</s>
<s>
Heritrix	B-Application
includes	O
a	O
command-line	B-Application
tool	I-Application
called	O
arcreader	O
which	O
can	O
be	O
used	O
to	O
extract	O
the	O
contents	O
of	O
an	O
Arc	B-Application
file	I-Application
.	O
</s>
<s>
The	O
following	O
command	O
lists	O
all	O
the	O
URLs	O
and	O
metadata	O
stored	O
in	O
the	O
given	O
Arc	B-Application
file	I-Application
(	O
in	O
format	O
)	O
:	O
</s>
<s>
Heritrix	B-Application
comes	O
with	O
several	O
command-line	B-Application
tools	I-Application
:	O
</s>
