Step One
Find an EXISTING dragon that has the genes you're looking to compare.
Step Two
Enter its ID into the FORSEE PROGENY, then enter my Whistletone (#76739076) into the other. Hit preview. Right click on each baby and copy the link, then paste it into each of the below boxes. Repeat this until you've filled as many boxes as you feel is necessary. More babies means higher accuracy.
Step Three
Hit calculate once you're happy with the number of babies to see how rare the program thinks the gene likely is.
Calculations will be here.
How this works:
First things first, it doesn't ping FR's servers in any way. Now, Whistletone has all Limited (4/5) rarity genes, which have a unique rarity depending on the rarity of the breed her partner has. Additionally, I have a database that I created of every flight rising gene and the number it corresponds to. When you put in the scry link for a baby, I'm able to figure out whether they are Whistetone's gene, or if they are Not. And I just count up how many for each. That count, compared to the total number of babies in here, gives me a percent. I compare that percent against my known percentages for genes of different rarities, then boom I have my predicted rarity for the new gene.