• Fix #110: Counts for ‘too short’ and ‘too long’ reads were swapped in statistics.
  • Fix #115: Make --trim-n work also on second read for paired-end data.


  • Support single-pass paired-end trimming with the new -A/-G/-B/-U parameters. These work just like their -a/-g/-b/-u counterparts, but they specify sequences that are removed from the second read in a pair.

    Also, if you start using one of those options, the read modification options such as -q (quality trimming) are applied to both reads. For backwards compatibility, read modifications are applied to the first read only if neither of -A/-G/-B/-U is used. See the documentation for details.

    This feature has not been extensively tested, so please give feedback if something does not work.

  • The report output has been re-worked in order to accomodate the new paired-end trimming mode. This also changes the way the report looks like in single-end mode. It is hopefully now more accessible.

  • Chris Mitchell contributed a patch adding two new options: --trim-n removes any N bases from the read ends, and the --max-n option can be used to filter out reads with too many N.

  • Support notation for repeated bases in the adapter sequence: Write A{10} instead of AAAAAAAAAA. Useful for poly-A trimming: Use -a A{100} to get the longest possible tail.

  • Quality trimming at the 5’ end of reads is now supported. Use -q 15,10 to trim the 5’ end with a cutoff of 15 and the 3’ end with a cutoff of 10.

  • Fix incorrectly reported statistics (> 100% trimmed bases) when --times set to a value greater than one.

  • Support .xz-compressed files (if running in Python 3.3 or later).

  • Started to use the GitHub issue tracker instead of Google Code. All old issues have been moved.


  • IUPAC characters are now supported. For example, use -a YACGT for an adapter that matches both CACGT and TACGT with zero errors. Disable with -N. By default, IUPAC characters in the read are not interpreted in order to avoid matches in reads that consist of many (low-quality) N bases. Use --match-read-wildcards to enable them also in the read.
  • Support for demultiplexing was added. This means that reads can be written to different files depending on which adapter was found. See the section in the documentation for how to use it. This is currently only supported for single-end reads.
  • Add support for anchored 3’ adapters. Append $ to the adapter sequence to force the adapter to appear in the end of the read (as a suffix). Closes issue #81.
  • Option --cut (-u) can now be specified twice, once for each end of the read. Thanks to Rasmus Borup Hansen for the patch!
  • Options --minimum-length/--maximum-length (-m/-M) can be used standalone. That is, cutadapt can be used to filter reads by length without trimming adapters.
  • Fix bug: Adapters read from a FASTA file can now be anchored.


  • Fix bug: Ensure --format=... can be used even with paired-end input.
  • Fix bug: Sometimes output files would be incomplete because they were not closed correctly.
  • Alignment algorithm is a tiny bit faster.
  • Extensive work on the documentation. It’s now available at .
  • For 3’ adapters, statistics about the bases preceding the trimmed adapter are collected and printed. If one of the bases is overrepresented, a warning is shown since this points to an incomplete adapter sequence. This happens, for example, when a TruSeq adapter is used but the A overhang is not taken into account when running cutadapt.
  • Due to code cleanup, there is a change in behavior: If you use --discard-trimmed or --discard-untrimmed in combination with --too-short-output or --too-long-output, then cutadapt now writes also the discarded reads to the output files given by the --too-short or --too-long options. If anyone complains, I will consider reverting this.
  • Galaxy support files are now in a separate repository.


  • Adapter sequences can now be read from a FASTA file. For example, write -a file:adapters.fasta to read 3’ adapters from adapters.fasta. This works also for -b and -g.
  • Add the option --mask-adapter, which can be used to not remove adapters, but to instead mask them with N characters. Thanks to Vittorio Zamboni for contributing this feature!
  • U characters in the adapter sequence are automatically converted to T.
  • Do not run Cython at installation time unless the –cython option is provided.
  • Add the option -u/–cut, which can be used to unconditionally remove a number of bases from the beginning or end of each read.
  • Make --zero-cap the default for colorspace reads.
  • When the new option --quiet is used, no report is printed after all reads have been processed.
  • When processing paired-end reads, cutadapt now checks whether the reads are properly paired.
  • To properly handle paired-end reads, an option –untrimmed-paired-output was added.


  • This release of cutadapt reduces the overhead of reading and writing files. On my test data set, a typical run of cutadapt (with a single adapter) takes 40% less time due to the following two changes.
  • Reading and writing of FASTQ files is faster (thanks to Cython).
  • Reading and writing of gzipped files is faster (up to 2x) on systems where the gzip program is available.
  • The quality trimming function is four times faster (also due to Cython).
  • Fix the statistics output for 3’ colorspace adapters: The reported lengths were one too short. Thanks to Frank Wessely for reporting this.
  • Support the --no-indels option. This disallows insertions and deletions while aligning the adapter. Currently, the option is only available for anchored 5’ adapters. This fixes issue 69.
  • As a sideeffect of implementing the –no-indels option: For colorspace, the length of a read (for --minimum-length and --maximum-length) is now computed after primer base removal (when --trim-primer is specified).
  • Added one column to the info file that contains the name of the found adapter.
  • Add an explanation about colorspace ambiguity to the README


  • Preliminary paired-end support with the --paired-output option (contributed by James Casbon). See the README section on how to use it.
  • Improved statistics.
  • Fix incorrectly reported amount of quality-trimmed Mbp (issue 57, fix by Chris Penkett)
  • Add the --too-long-output option.
  • Add the --no-trim option, contributed by Dave Lawrence.
  • Port handwritten C alignment module to Cython.
  • Fix the --rest-file option (issue 56)
  • Slightly speed up alignment of 5’ adapters.
  • Support bzip2-compressed files.


  • At least 25% faster processing of .csfasta/.qual files due to faster parser.
  • Between 10% and 30% faster writing of gzip-compressed output files.
  • Support 5’ adapters in colorspace, even when no primer trimming is requested.
  • Add the --info-file option, which has a line for each found adapter.
  • Named adapters are possible. Usage: -a My_Adapter=ACCGTA assigns the name “My_adapter”.
  • Improve alignment algorithm for better poly-A trimming when there are sequencing errors. Previously, not the longest possible poly-A tail would be trimmed.
  • James Casbon contributed the --discard-untrimmed option.


  • Allow to “anchor” 5’ adapters (-g), forcing them to be a prefix of the read. To use this, add the special character ^ to the beginning of the adapter sequence.
  • Add the “-N” option, which allows ‘N’ characters within adapters to match literally.
  • Speedup of approx. 25% when reading from .gz files and using Python 2.7.
  • Allow to only trim qualities when no adapter is given on the command-line.
  • Add a patch by James Casbon: include read names (ids) in rest file
  • Use nosetest for testing. To run, install nose and run “nosetests”.
  • When using cutadapt without installing it, you now need to run bin/cutadapt due to a new directory layout.
  • Allow to give a colorspace adapter in basespace (gets automatically converted).
  • Allow to search for 5’ adapters (those specified with -g) in colorspace.
  • Speed up the alignment by a factor of at least 3 by using Ukkonen’s algorithm. The total runtime decreases by about 30% in the tested cases.
  • allow to deal with colorspace FASTQ files from the SRA that contain a fake additional quality in the beginning (use --format sra-fastq)


  • ASCII-encoded quality values were assumed to be encoded as ascii(quality+33). With the new parameter --quality-base, this can be changed to ascii(quality+64), as used in some versions of the Illumina pipeline. (Fixes issue 7.)
  • Allow to specify that adapters were ligated to the 5’ end of reads. This change is based on a patch contributed by James Casbon.
  • Due to cutadapt being published in EMBnet.journal, I found it appropriate to call this release version 1.0. Please see for the article and I would be glad if you cite it.
  • Add Galaxy support, contributed by Lance Parsons.
  • Patch by James Casbon: Allow N wildcards in read or adapter or both. Wildcard matching of ‘N’s in the adapter is always done. If ‘N’s within reads should also match without counting as error, this needs to be explicitly requested via --match-read-wildcards.


  • Fix issue 20: Make the report go to standard output when -o/--output is specified.

  • Recognize .fq as an extension for FASTQ files

  • many more unit tests

  • The alignment algorithm has changed. It will now find some adapters that previously were missed. Note that this will produce different output than older cutadapt versions!

    Before this change, finding an adapter would work as follows:

    • Find an alignment between adapter and read – longer alignments are better.
    • If the number of errors in the alignment (divided by length) is above the maximum error rate, report the adapter as not being found.

    Sometimes, the long alignment that is found had too many errors, but a shorter alignment would not. The adapter was then incorrectly seen as “not found”. The new alignment algorithm checks the error rate while aligning and only reports alignments that do not have too many errors.


  • now compatible with Python 3
  • Add the --zero-cap option, which changes negative quality values to zero. This is a workaround to avoid segmentation faults in BWA. The option is now enabled by default when --bwa/--maq is used.
  • Lots of unit tests added. Run them with cd tests && ./
  • Fix issue 16: --discard-trimmed did not work.
  • Allow to override auto-detection of input file format with the new -f/--format parameter. This mostly fixes issue 12.
  • Don’t break when input file is empty.


  • Install a single cutadapt Python package instead of multiple Python modules. This avoids cluttering the global namespace and should lead to less problems with other Python modules. Thanks to Steve Lianoglou for pointing this out to me!
  • ignore case (ACGT vs acgt) when comparing the adapter with the read sequence
  • .FASTA/.QUAL files (not necessarily colorspace) can now be read (some 454 software uses this format)
  • Move some functions into their own modules
  • lots of refactoring: replace the fasta module with a much nicer seqio module.
  • allow to input FASTA/FASTQ on standard input (also FASTA/FASTQ is autodetected)


  • add --too-short-output and --untrimmed-output, based on patch by Paul Ryvkin (thanks!)
  • add --maximum-length parameter: discard reads longer than a specified length
  • group options by category in --help output
  • add --length-tag option. allows to fix read length in FASTA/Q comment lines (e.g., length=123 becomes length=58 after trimming) (requested by Paul Ryvkin)
  • add -q/--quality-cutoff option for trimming low-quality ends (uses the same algorithm as BWA)
  • some refactoring
  • the filename - is now interpreted as standard in or standard output


  • Change default behavior of searching for an adapter: The adapter is now assumed to be an adapter that has been ligated to the 3’ end. This should be the correct behavior for at least the SOLiD small RNA protocol (SREK) and also for the Illumina protocol. To get the old behavior, which uses a heuristic to determine whether the adapter was ligated to the 5’ or 3’ end and then trimmed the read accordingly, use the new -b (--anywhere) option.
  • Clear up how the statistics after processing all reads are printed.
  • Fix incorrect statistics. Adapters starting at pos. 0 were correctly trimmed, but not counted.
  • Modify scoring scheme: Improves trimming (some reads that should have been trimmed were not). Increases no. of trimmed reads in one of our SOLiD data sets from 36.5 to 37.6%.
  • Speed improvements (20% less runtime on my test data set).


  • Useful exit codes
  • Better error reporting when malformed files are encountered
  • Add --minimum-length parameter for discarding reads that are shorter than a specified length after trimming.
  • Generalize the alignment function a bit. This is preparation for supporting adapters that are specific to either the 5’ or 3’ end.
  • pure Python fallback for alignment function for when the C module cannot be used.


  • Support gzipped input and output.
  • Print timing information in statistics.


  • add --discard option which makes cutadapt discard reads in which an adapter occurs


  • (more) correctly deal with multiple adapters: If a long adapter matches with lots of errors, then this could lead to a a shorter adapter matching with few errors getting ignored.


  • fix huge memory usage (entire input file was unintentionally read into memory)


  • allow FASTQ input


  • initial release