New BLAST default parameters and search limits coming in September

To provide a more efficient BLAST experience for everyone, we’re changing some parameters and limits on the web BLAST service on September 8, 2020. The new settings, listed below, will improve overall performance and make search times more consistent.

  1. The Expect Value Threshold default setting will be reduced to 0.05.
  2. The maximum number of target sequences (Max target sequences) limit will be no more than 5,000.
  3. The maximum allowed query length for nucleotide queries (blastn, blastx, and tblastx) will be 1,000,000 and 100,000 for protein queries (blastp and tblastn).

These changes will help keep the BLAST service running smoothly as the already very large databases continue to grow rapidly. If you have any questions or concerns, please email us at blast-help@ncbi.nlm.nih.gov

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