i won't get any modifiers as i level my tool

probobly an old tool that you had before you installed Tinkers' Tool Leveling. You need to make a new too.
@mikolajww that is kind of irrelevant to this post, but you should always try tab completing before you ask.

I have the same issue with the modifiers. I've a Pickaxe on level 7 (Grandmaster) and can't add anymore modifiers. I've currently added a Diamond, Lapis, Redstone and Nether Quartz. Trying to add any other modifier in the tool forge shows "Not enough Modifiers (1 needed)".

Gonna close this since there never was any further information. @Programie open a new issue when you can reproduce it with a minimal mod set.

Just a small update: I've tested it again with a vanilla forge installation + Thinker's Construct + Tinker's Tool Leveling + Mantle (in the same versions as used by my used modpack) and it just works as expected.

After mining a while I was able to add multiple modifiers to my tool (additionally to the basic 3 modifiers). I was able to add diamond, Redstone, Lapis, Nether Quartz, Emerald and Blaze Powder without any issue.

The only difference: I used a Cobalt tool (Cobalt Hammer) instead of a Steel one, because Steel was not available in this combination of mods (I guess Steel is added by another mod). I hope the issue is not caused by using a Steel tool.

Edit: Also works fine with the Steel Hammer.

Edit 2: I just found out it, for me it was just a misunderstanding how modifiers work. Every upgrade of a modifier also requires another modifier slot. For example, for Luck III, 3 modifiers are required instead of just one. In my test I added each modifier for one time only (Luck I, etc.) which resulted in having more modifiers remaining than when having all modifiers maxed out.

What versions, try reproducing with only TiC, mantle and TTL in a new world.

Is there a command/way to add levels to a tool? I lost my high level tool due to a stupid accident and don't want to start from the beginning.