I am not aware of an official fasta format description. The only constraint that I know of is that there should not be any whitespace after >. Apart from that particular position, whitespaces are allowed in the header line.

So, regarding your particular example, both are valid fasta sequences. When in doubt, you can use SeqIO from Biopython, if you can parse your file with the following code, it is should be a valid fasta file.

from Bio import SeqIO

with open("example.fasta") as handle:
    for record in SeqIO.parse(handle, "fasta"):
        print(record.id)

Edit per @Chris_Rands' comment

The code below does the same as above, meaning that SeqIO.parse() takes care of opening and closing the file.

from Bio import SeqIO

for record in SeqIO.parse("example.fasta", "fasta"):
    print(record.id)

I am not aware of an official fasta format description. The only constraint that I know of is that there should not be any whitespace after >. Apart from that particular position, whitespaces are allowed in the header line.

So, regarding your particular example, both are valid fasta sequences. When in doubt, you can use SeqIO from Biopython, if you can parse your file with the following code, it is should be a valid fasta file.

from Bio import SeqIO

with open("example.fasta") as handle:
    for record in SeqIO.parse(handle, "fasta"):
        print(record.id)

Edit per @Chris_Rands' comment

The code below does the same as above, meaning that SeqIO.parse() takes care of opening and closing the file.

from Bio import SeqIO

for record in SeqIO.parse("example.fasta", "fasta"):
    print(record.id)

I am not aware of an official fasta format description. The only constraint that I know of is that there should not be any whitespace after >. Apart from that particular position, whitespaces are allowed in the header line.

So, regarding your particular example, both are valid fasta sequences. When in doubt, you can use SeqIO from Biopython, if you can parse your file with the following code, it is a valid fasta file.

from Bio import SeqIO

with open("example.fasta") as handle:
    for record in SeqIO.parse(handle, "fasta"):
        print(record.id)

I am not aware of an official fasta format description. The only constraint that I know of is that there should not be any whitespace after >. Apart from that particular position, whitespaces are allowed in the header line.

So, regarding your particular example, both are valid fasta sequences. When in doubt, you can use SeqIO from Biopython, if you can parse your file with the following code, it is should be a valid fasta file.

from Bio import SeqIO

with open("example.fasta") as handle:
    for record in SeqIO.parse(handle, "fasta"):
        print(record.id)

Edit per @Chris_Rands' comment

The code below does the same as above, meaning that SeqIO.parse() takes care of opening and closing the file.

from Bio import SeqIO

for record in SeqIO.parse("example.fasta", "fasta"):
    print(record.id)