In Pokémon GO, each Pokémon can be appraised by your Team Leader. In the past they would give you some cryptic response, like "its stats are the best it can be!" or "its stats are crap... but hey, it's still your friend and it still loves you and it really doesn't want to be transferred to the Professor"... but eventually it was replaced by a graph system which straight up tells you what its IVs are. Although it was fun trying to work out what your Pokémon's stats are, this method at least helps kill a lot of calculating time.
So wait... "stats"? "IVs"?? What is all of this to begin with? Well, if every Pokémon were EXACTLY the same, then the game would be boring. So every single Pokémon has some variety in its three stats: Attack, Defense, and HP. This variety is a number between 0 and 15, such that—if all things were the same—Pokémon with a 0 for that stat will be weaker than a Pokémon with a 15 for that same stat. So in trying to get powerful Pokémon, you'll need to try to get a Pokémon with 15's in all three of its stats.
Now the Appraisal System in Pokémon GO shows four different values: the Stats Rating for your Pokémon, one rating for each of the three stats (Attack, Defense, HP), and a "Star" Rating, which rates your Pokémon between zero and three stars according to the total added value of the Stats Rating. Pretty simple, huh? Therefore, the goal of this page is to show you how to decipher the Stats and Stars rating, as well as give you a way to name your Pokémon as a way to help you sort through them all.
Stats Rating
Each stat is a number between 0 and 15. This is based on the fact that its stats are encoded using hexadecimal notation. This means when an number counts up in hexadecimal, when it reaches the tenth value, it doesn't write it as "10", but as "A". Eleven is "B", Twelve is "C", and so on. When it finally reached sixteen, it then rolls over to "10"; this then means "11" in hexadecimal is actually seventeen, "12" is eighteen, etc.
Now if that is a bit complex, don't worry about it. Basically consider any letters used as a "codeword" for a large number. If it helps, in the below chart, I've listed all possible values for the stats, just so you can have a handy lookup table to determine how good or bad your Pokémon's stats are. Just remember that the "HEX" column means "Hexadecimal", while "DEC" is the normal "decimal" notation.
Stats Rating  HEX  DEC  Notes 
0  0  
1  1  
2  2  
3  3  
4  4  
5  5  
6  6  
7  7  
8  8  
9  9  
A  10  
B  11  
C  12  
D  13  
E  14  
F  15 
Simple, huh?
Now one reason I included the Hexadecimal notation is to help give you a way to easily organize your Pokémon based on its stats. For example, if a Pokémon has 10 for Attack, 12 for Defense, and 7 for HP, you could write it out as AC7, which "A" = 10 and "C" = 12. Best of all, since your Pokémon can be listed in alphabetical order, using this format ensures that your best Pokémon will be closer to the bottom of the list. Nifty, huh?
Finally, to get a nice, single number to determine your Pokémon's value, simply add up all the numbers in that Pokémon's stats. Therefore, for the example Pokémon stats I listed above, the total value would be 29. Simple, huh? Knowing this, you can then understand how it can be used to determine it's Star Rating below.
Stats Rating
Now that you know how to get a single number value for your Pokémon's stats, you can understand how the "Star" Rating system is based on that.
In the chart below, "MIN" means minimum total stat value which earns that Star rating, while "MAX" means the maximum value instead.
Star Rating  MIN  MAX  Notes 
00 (00%)  22 (49%)  Basically covers every Pokémon with total stat values less than 50%. Let's face it, the only one that's gonna love these guys are their Mothers. And Fathers too, nothing saying that they can't! • Low Example • High Example 

23 (51%)  29 (65%)  Covers every Pokémon with total stat values between 50% and 66.66% • Low Example • High Example 

30 (67%)  36 (80%)  Any Pokémon in the top 1/3 but not at good as the top 1/5 are given 2 stars. • Low Example • High Example 

37 (82%)  44 (98%)  Three star Pokémon are in the top (20) percentage, like Joey's Rattata. • Low Example • High ExampleThat said, sometimes a Pokémon can have a total stat value outside of this range, like it should have a two star rating, but still be given three stars. Why this is is still being investigated. 

45 (100%)  45 (100%)  Only the best of the best, as in Pokémon with the absolute best stats, are given this Redtinted Threestar rating. • Example 
At least this way you can use the stars to determine how good your Pokémon are at a glance. If it has three stars, then at least you'll know that none of your Pokémon's stats will be anything worse than a 7 out of 15, which is around the middle for that stat.
Name Calculator
Now that you understand how the stats work and how to read the values, below is a handy little utility to help you create a name for your Pokémon to aid in organization. The idea here is that, when you input your Pokémon's three stats, it will give you a single five letter/digit code which you can use to name your Pokémon. Doing this will then give you a way to ensure that all of your best Pokémon are listed at the bottom of the "Name" list (which is in Alphabetical order).
For reference, the five digit code is in the format of: XXADH
 XX — a two digit value which is the overall value rating for your Pokémon.
 A — attack stat, in Hexadecimal (ie A = 10, B = 11, ... F = 15)
 D — defense stat, likewise in hex
 H — HP stat, likewise in hex
The XX value can in turn be in two forms, either:
 out of 45, which is the total possible values of your Pokémon's stats (ie 15 + 15 + 15), or,
 out of 100, which is a percentage of that total possible value
 For example, 29 total value is 64.444% of 45, and so it would be listed as simply "64".
Here's a quick example of the kind of ordering this utility can help you see in order to help with organization:
 22046 — 22%; Attack = 0, Defense = 4, HP = 6
 49C82
 64FD1
 71BBA — 71%; Attack = 11 (B in hex), Defense = 11 (B in hex), HP = 10 (A in hex)
 71C6E — 71%; Attack = 12 (C in hex), Defense = 6, HP = 14 (E in hex)
 807EF
 84EDB
 91FBF
 96EFE — 96%; Attack = 14/E, Defense = 15/F, HP = 14/E
 99FFF — 100%; Attack, Defense, HP = 15/F
In order to keep things workable, two minor changes have been made to the utility:
 Any total stat value which gives you a 68.8888% (thus rounded to 69%) value is instead rounded down to 68%, in order to avoid Pokémon GO's vulgar word filter.
 In the case of a Pokémon with all 15 for its stats and thus has a 100% value, it's instead listed as 99%, only because you can't fit 100% into two characters.
That's about it! Enjoy!
(Utility is still under construction. Sorry!)
Hum.
Anyways, note to self:
 write appraisal calculator and name generator
 make sure "69" is not generated
Ok.