Getting the most from support gems in Path of Exile 2
How support gems work in PoE2: support sockets, tiers, lineage supports, supports with hidden costs, and how to test which ones help your skill.
Supports modify one skill
In Path of Exile 2, support gems go into sockets on the skill gem itself rather than into your gear. Each support changes only the skill it's socketed into, so the same support can do a lot for one skill and nothing for another.
A skill gem starts with a few support sockets, and 
Jeweller's Orbs add more. Because sockets are limited, the question for every support is whether it beats the alternative in that socket.
Tiers and lineage supports
Many supports come in tiers (I, II, III). Higher tiers are stronger versions of the same effect and usually need a higher level of uncut support gem to cut.
Lineage supports are named, unique-like supports - 
Rakiata's Flow, 
Dominus' Grasp, 
Dialla's Desire. They're often build-defining and priced to match. Check whether your build actually uses what makes one special before paying for it.
Supports with hidden costs
Some supports come with a downside that Path of Building doesn't fully count:
- Supports that stop your skill inflicting an ailment (like
Elemental Focus) can break anything that depends on that ailment - 
Mana Remnants and 
Cast on Elemental Ailment both need shocks, freezes or ignites - Rakiata's Flow makes hits treat enemy elemental resistances as inverted, which works against Exposure and other resistance reduction on that skill
- Some supports drain life, energy shield or mana on use, or use up flask charges
Close Combat rewards being near enemies, which a ranged skill rarely is
PoE MVP's support gem tab flags these instead of listing them as the top pick.
Meta gems and their supports
Meta gems like 
Cast on Critical and Cast on Elemental Ailment trigger the spells socketed into them when they fill with energy. Supports like 
Boundless Energy and 
Energy Retention make them fill faster or refund energy, which means more triggers.
Not every spell can go into every meta gem - if one won't fit, cast it yourself or use a different trigger.
Testing what helps
The reliable way to choose supports is to test them: swap each candidate into the socket in Path of Building and compare. Check the ladder for what other players use with your skill, then measure it on your own character - popular isn't the same as best for you.
PoE MVP tries every support gem you could use in each socket of your main skill and ranks them by what they add, with the hidden costs called out.