JEC is an addon to JEI making the items appear dynamically when you discover and interact with them in the world.

You spawn in knowing no items

You spawn into the world not knowing of any items, as you interact with items or fluids they gradually fill out your JEI catalogue.

The mod is client only and is not required on the server.

FAQ

I've comprehended an oak log, why can't I see what it crafts?

But have you comprehended crafting?

Can I include JEC in my mod pack?

Of course!

Is JEC client-only?

Yes, in 1.21.1 recipes are stored client side, so all discoveries and logic are client side.

I have an issue / bug / crash / report / request, where can I send it?

JEC Github Issues page

Configs:

All of the discovery logic is configurable.

Config options

Hide Undiscovered Items\ Toggles whether undiscovered items are pulled out of JEI entirely, or only their recipes are locked.\ On, JEI starts empty and fills in as you find things; off, every item stays listed and just the recipes are hidden.

Require Outputs Discovered\ Toggles whether you also need to have held a recipe's result before the recipe shows up.\ Knowing every ingredient for a cake isn't enough — you'd need to have picked up a cake at least once too.

Granular Subtype Discovery\ Toggles whether enchanted books and potions unlock one variant at a time instead of all at once.\ Finding a Sharpness book reveals only that book, not every enchant in the game; a Night Vision potion reveals only Night Vision.

Hide Undiscovered Fluids\ Toggles whether fluids stay out of JEI's fluid list until you've met them.\ Water and lava don't show up until you've waded through them or grabbed a bucket of them.

Discover Base Container\ Toggles whether grabbing a "filled" item also teaches the empty thing it's made from.\ A water bucket also unlocks the empty bucket, a potion unlocks the glass bottle, and a bowl of soup unlocks the bowl.

Discover Fluids By Wading\ Toggles whether standing in a fluid counts as discovering it.\ Step into a lake and water unlocks; take a dip in lava and lava unlocks (good luck).

Discover Fluids By Bucket\ Toggles whether holding a bucket of a fluid counts as discovering it.\ A lava bucket sitting in your inventory unlocks lava without you ever touching the real stuff.

Unresolved Recipe Policy\ Decides what happens to modded recipes whose ingredients the mod can't read — keep them showing, or keep them hidden.\ A strange modded machine recipe either always stays visible (REVEAL) or stays locked like everything else (HIDE).

Discovery Scope\ Chooses whether your discoveries are tracked per world or shared across all of them.\ PER_SAVE starts every new world from scratch; GLOBAL carries everything you've found between worlds.

Scan Interval Ticks\ Sets how often the mod checks your inventory for newly held items.\ At the default 10 (half a second) things unlock almost instantly; turn it up to scan less often on massive packs.

Reveal All\ Debug switch that unhides everything at once.\ Flip it on to check JEI is working, or to switch the whole mod off without uninstalling it.

Log Stats\ Toggles whether the mod writes indexing and gating numbers to your log.\ Off by default so it doesn't clutter your latest.log; handy if something's misbehaving.

JEI -Just Enough Comprehension (JEC)