Primer3 Input May 2026

SEQUENCE_INTERNAL_OLIGO_MIN_SIZE=18 SEQUENCE_INTERNAL_OLIGO_OPT_TM=55.0 Save this as my_primers.txt :

PRIMER_MIN_SIZE=18 PRIMER_OPT_SIZE=20 PRIMER_MAX_SIZE=25

SEQUENCE_ID=TP53_exon7_test SEQUENCE_TEMPLATE=GGACCTGGTCCTCTGACTGCTCTTTTCACCCATCTACAGTCCCCCTTGCCGTCCCAAGCAATGGATGATTTGATGCTGTCCCCGGACGATATTGAACAATGGTTCACTGAAGACCCAGGTCCAGATGAAGCTCCCAGAATGCCAGAGGCTGCTCCCCGCGTGGCCCCTGCACCAGCAGCTCCTACACCGGCGGCCCCTGCACCAGCCCCCTCCTGGCCCCTGTCATCTTCTGTCCCTTCCCAGAAAACCTACCAGGGCAGCTACGGTTTCCGTCTGGGCTTCTTGCATTCTGGGACAGCCAAGTCTGTGACTTGCACGGTCAGTTGCCCTGAGGGGCTGGCTTCCATGAGACTTCAT PRIMER_TASK=pick_pcr_primers SEQUENCE_TARGET=120,1 primer3 input

PRIMER_MAX_POLY_X=4 # Max mononucleotide repeats (e.g., AAAA) PRIMER_GC_CLAMP=1 # Require G or C in last 5 bases of 3' end PRIMER_MAX_SELF_ANY=4.0 PRIMER_MAX_SELF_END=3.0 PRIMER_NUM_RETURN=5

Today, we are tearing down the primer3_core input file. Primer3 input is plain text. It uses a simple KEY=VALUE syntax. The engine reads these parameters, processes the sequence, and spits out the best primers. The engine reads these parameters, processes the sequence,

Next time you are frustrated that "no primers were found," don't tweak the sequence—. Loosen the Tm range by 1°C or extend the product size range. The perfect primer pair is always just a parameter change away. Have a tricky multiplexing scenario? Drop the parameters in the comments below.

PRIMER_PRODUCT_SIZE_RANGE=150-250 PRIMER_PRODUCT_OPT_SIZE=200 The perfect primer pair is always just a

But Primer3 is not a "point-and-click" black box. It is a . To unlock its full potential, you must understand its input format.