Open FASTQ files in your browser
The reads a sequencer writes, each with a quality for every letter. Open a FASTQ right here as a row for each read. Nothing leaves your device.
Or drop it anywhere on this page
What you'll see
Your reads open as a row for each one, the first rows on show while the rest are read.
- A row for each read • Length, GC and mean quality
- Sort and filter • Counts for every column
- Show details • Reads, bases and the qualities' encoding
- Export • Save as CSV, Excel, JSON or Parquet
About FASTQ
Illumina's, Oxford Nanopore's and PacBio's sequencers all hand out their reads as FASTQ, which the Wellcome Trust Sanger Institute made by adding a quality for each letter to FASTA. A run's files, usually gzipped, can hold hundreds of millions of reads.
Each read takes four lines: @ and its name, its letters, a + line, and a quality for each letter as one character, its Phred score plus 33, so I means 40, one wrong letter in 10,000. Paired reads come as two files, R1 and R2, in the same order.
Filepeek reads the file in pieces in your browser and shows each read as a row with its name, length, GC content and mean quality, its letters and qualities beside them, to sort, search and filter like any table. Show details gives the number of reads and letters, their lengths and the qualities' encoding, and Export saves the rows as CSV, Excel, JSON or Parquet.
FASTQ sequencing reads
.fastq • .fq
Format
- MIME type
- text/x-fastq
- Made by
- The Wellcome Trust Sanger Institute
Inside the file
- Each read
- Four lines
- Lines
- Name, letters, a +, qualities
- Qualities
- Phred scores, one character each
- Written by
- Illumina, Nanopore and PacBio sequencers
Opens in every browser
Filepeek opens FASTQ files of any size in Chrome, Edge, Firefox and Safari, read in pieces so the first reads show at once. On their own, browsers download them.
- YouChromeOpens through Filepeek
- YouEdgeOpens through Filepeek
- YouFirefoxOpens through Filepeek
- YouSafariOpens through Filepeek
Apps that open FASTQ
- WindowsNo app built in reads it • FastQC and UGENE do
- MacNo app built in reads it • FastQC and UGENE do
- iPhone and iPadNo app opens it
- AndroidNo app opens it
Questions
How do I open a .fastq.gz file?
Drop it here as it is. Filepeek unpacks the FASTQ inside and opens its reads right away.
What do the quality characters mean?
Each is a Phred score plus 33 as a character: ! is 0, + is 10, 5 is 20, ? is 30 and I is 40, and 10, 20, 30 and 40 mean one wrong letter in 10, 100, 1,000 and 10,000. Very old Illumina files add 64, and Filepeek tells them apart by their range.
Can I check how good a run is?
Sort by Mean quality to see the worst reads first, or by Length for the shortest, and Show details gives the run's read lengths and its lowest and highest quality. For a full report, FastQC is the usual tool.
Why do my reads come in two files?
Paired-end sequencing reads each fragment from both ends, and the sequencer writes the first reads to the R1 file and the second to R2, in the same order, so their names match row for row.