4/24 update: Added the recommended recipes infographic.
T-Doll Production is the primary “gacha” mechanic in Girls’ Frontline and one of the main keys to progressing in the game.
Unlike most other gacha systems, T-Doll Production does not rely on a premium currency, but rather four farmable in-game Resources (Manpower, Ammo, Rations, Parts).
T-Doll Production outputs a random result based on the total amount and ratio of Resources committed. This system allows players to “manipulate” the gacha to a certain extent, as each class of T-Doll can only be found within a certain range of spent resources.
According to an official statement from Digital Sky, the construction rates for each rarity are as follows:
The production rates are actually much higher in practice, especially for T-Doll classes that contain a large number of 5★ units such as ARs. It's likely that MICA slightly increases the total pull rate of high-rarity units with newly added T-Dolls to keep older dolls obtainable, as Girls' Frontline does not typically run rate-up events for previously-released T-Dolls.
As previously stated, the class of T-Doll obtained is related to the amount of resources used in crafting.
Roughly speaking, HGs are crafted using the lowest amount of resources, SMGs, ARs, and RFs are crafted using a moderate amount, and MGs are crafted using the highest amount of resources.
Using a higher amount of resources in crafting does not necessarily guarantee a higher rarity T-Doll, however, so don’t waste your resources! There are specific recommended recipes with high pull rates that you should use instead.
There are unspecified resource limits in the game that dictate the chances of being able to obtain specific classes of weapons. The primary resource thresholds are a total of 800 across all four resources, which is the lower resource limit for producing ARs, and 920 across all resources, which is the upper resource limit for producing HGs.
This means that if you do not commit at least 800 total resources (in any combination) to construction, there is zero chance to get an AR, and if you commit more than 920 total resources, there is zero chance to get an HG.
Although there are resource limits for producing specific classes, there are no known formulas for using specific amounts of each resource to guarantee a specific weapon or weapon type.
The “recipes” for each weapon class given in the following sections have been confirmed to generally obtain specific classes of weapons, but other recipes that satisfy the minimum requirements also work. Players are encouraged to tweak these recipes slightly or experiment with different recipes for their own curiosity and enjoyment.
Here's a handy infographic summarizing the recommended crafting recipes from the GFL Explained: Rate-Up guide.
The recipes listed here are the widely known cost-efficient recipes, meaning that they maximize the ratio of high-rarity T-Dolls pulled relative to the cost of resources/contracts spent.
Each recipe may not exclusively yield the class of weapon listed, and these recipes do not guarantee 4- or 5-star T-Dolls since T-Doll Production is still a gacha mechanic with no pity/welfare system.
There are also in-game recipes that you can find in the factory; commanders are free to attempt those recipes as well, should they want some variety from the recommended recipes on this page.