PRIMER_MIN_SIZE (int)
Minimum acceptable length of a primer. Must be greater than 0 and less than or equal to PRIMER_MAX_SIZE.

PRIMER_OPT_SIZE (int)
Optimum length (in bases) of a primer. Primer3 will attempt to pick primers close to this length.

PRIMER_MAX_SIZE (int)
Maximum acceptable length (in bases) of a primer. Currently this parameter cannot be larger than 35. This limit is governed by maximum oligo size for which Primer3's melting-temperature is valid.

PRIMER_MIN_TM (float)
Minimum acceptable melting temperature (Celsius) for a primer oligo.

PRIMER_OPT_TM (float)
Optimum melting temperature (Celsius) for a primer. Primer3 will try to pick primers with melting temperatures are close to this temperature. The oligo melting temperature formula used can be specified by user. Please see PRIMER_TM_FORMULA for more information.

PRIMER_MAX_TM (float)
Maximum acceptable melting temperature (Celsius) for a primer oligo.

PRIMER_PAIR_MAX_DIFF_TM (float)
Maximum acceptable (unsigned) difference between the melting temperatures of the left and right primers.

PRIMER_MIN_GC (float)
Minimum allowable percentage of Gs and Cs in any primer.

PRIMER_OPT_GC_PERCENT (float)
Optimum GC percent. This parameter influences primer selection only if PRIMER_WT_GC_PERCENT_GT or PRIMER_WT_GC_PERCENT_LT are non-0.

PRIMER_MAX_GC (float)
Maximum allowable percentage of Gs and Cs in any primer generated by Primer.

PRIMER_MIN_GC (float)
Minimum allowable percentage of Gs and Cs in any primer.

PRIMER_OPT_GC_PERCENT (float)
Optimum GC percent. This parameter influences primer selection only if PRIMER_WT_GC_PERCENT_GT or PRIMER_WT_GC_PERCENT_LT are non-0.

PRIMER_MAX_GC (float)
Maximum allowable percentage of Gs and Cs in any primer generated by Primer.

PRIMER_PRODUCT_SIZE_RANGE (size range list)
The associated values specify the lengths of the product that the user wants the primers to create, and is a space separated list of elements of the form - where an - pair is a legal range of lengths for the product. For example, if one wants PCR products to be between 100 to 150 bases (inclusive) then one would set this parameter to 100-150. If one desires PCR products in either the range from 100 to 150 bases or in the range from 200 to 250 bases then one would set this parameter to 100-150 200-250. Primer3 favors product-size ranges to the left side of the parameter string. Primer3 will return legal primers pairs in the first range regardless the value of the objective function for pairs in subsequent ranges. Only if there are an insufficient number of primers in the first range will Primer3 return primers in a subsequent range. For those with primarily a computational background, the PCR product size is the size (in base pairs) of the DNA fragment that would be produced by the PCR reaction on the given sequence template. This would, of course, include the primers themselves.

PRIMER_NUM_RETURN (int)
The maximum number of primer (pairs) to return. Primer pairs returned are sorted by their "quality", in other words by the value of the objective function (where a lower number indicates a better primer pair). Caution: setting this parameter to a large value will increase running time.

PRIMER_MAX_END_STABILITY (float, 999.9999)
The maximum stability for the last five 3' bases of a left or right primer. Bigger numbers mean more stable 3' ends. The value is the maximum delta G (kcal/mol) for duplex disruption for the five 3' bases as calculated using the nearest-neighbor parameter values specified by the option of PRIMER_TM_FORMULA For example if the table of thermodynamic parameters suggested by SantaLucia 1998, DOI:10.1073/pnas.95.4.1460 is used the deltaG values for the most stable and for the most labile 5mer duplex are 6.86 kcal/mol (GCGCG) and 0.86 kcal/mol (TATAT) respectively. If the table of thermodynamic parameters suggested by Breslauer et al. 1986, 10.1073/pnas.83.11.3746 is used the deltaG values for the most stable and for the most labile 5mer are 13.4 kcal/mol (GCGCG) and 4.6 kcal/mol (TATAC) respectively.