Making an item for a player that is a warlock of Dendar (who is very different in my setting) , does this seem balanced and also interesting for a level six player? Tried emulating a dagger of venom a little bit, they are a hexblade warlock. 

You have a +1 bonus to attack and damage rolls made with this magic weapon.

While attuned to this weapon it gains the following properties:
- You may speak its command word "venom" and cause poison to drip from its blade, on a successful hit a creature must beat your spell save DC or take an additional 1d10 poison damage. This effect last for one minute and after being used in this way cannot be used again until next midnight. 

Does the command word take an action? Bonus action? How many times can you use it?

It might be cool to have it require the word venom in Primordial.  If they don't know primordial, make a side quest to learn the word.  In addition to Inumiru's concerns, you should probably also say what saving throw the poison damage targets.

I'd consider rephrasing:

- You may speak its command word "venom" and cause poison to drip from its blade which requires no action. For one minute when you make a successful melee attack with this weapon, the target must on a successful hit a hit a creature must beat your succeed a constitution saving throw against your spell save DC or take an additional 1d10 poison damage. This effect last for one minute and after being used in  This way cannot be used again in this way until next midnight. 

Two things:

Firstly, I would simplify this to remove the constitution saving throw. It's only an additional 5 (1d10) damage per hit, and that involves the warlock choosing to get involved in the midst of the fighting rather than Eldritch Blasting, but it also just slows down combat. Endlessly making saving throws every time an attack hits, just to see if there's a small damage increase, seems like slowdown for no reason.

Does your warlock already use a Dagger or have an RP reason to? Personally if I was a Hexblade, with full access to Martial weapons, I'd hope to be using something that packed a bit more of a punch (a 1d8 weapon preferably). The base damage is just 1d4, plus an average 5.5 damage only if the target fails a Constitution saving throw. If the enemy fails the saving throw, the average weapon+poison damage will be 8. If the enemy makes the saving throw, the average damage will be 2.5. Compare that to a non-magical Greatsword (average damage 7), Greataxe (average damage 6.5), or a Halberd/Glaive (average damage 5.5 with 10ft reach) and even if the enemy is consistently failing its saving throw, the damage from this bespoke magical item will barely be out-pacing them - and even then, only if the target doesn't have poison immunity/resistance (which is very common). Hexblades can't use 2 handed weapons of course, but it's worthwhile when comparing it to other classes.

I'd drop the need for the saving throw altogether and change the damage to a bonus 1d10 poison damage on every hit, lasting 1 minute. This ups the average damage to 8 on every hit, with some good damage potential on a critical hit. I wouldn't put a 1d10 bonus on a Greatsword or Halberd, but on a dagger it's going to make it worth using.

Thanks! I am not great on the grammar behind magic items, makes it much clearer

Quote from Sanvael >>

Two things:

Firstly, I would simplify this to remove the constitution saving throw. It's only an additional 5 (1d10) damage per hit, and that involves the warlock choosing to get involved in the midst of the fighting rather than Eldritch Blasting, but it also just slows down combat. Endlessly making saving throws every time an attack hits, just to see if there's a small damage increase, seems like slowdown for no reason.

Does your warlock already use a Dagger or have an RP reason to? Personally if I was a Hexblade, with full access to Martial weapons, I'd hope to be using something that packed a bit more of a punch (a 1d8 weapon preferably). The base damage is just 1d4, plus an average 5.5 damage only if the target fails a Constitution saving throw. If the enemy fails the saving throw, the average weapon+poison damage will be 8. If the enemy makes the saving throw, the average damage will be 2.5. Compare that to a non-magical Greatsword (average damage 7), Greataxe (average damage 6.5), or a Halberd/Glaive (average damage 5.5 with 10ft reach) and even if the enemy is consistently failing its saving throw, the damage from this bespoke magical item will barely be out-pacing them - and even then, only if the target doesn't have poison immunity/resistance (which is very common). Hexblades can't use 2 handed weapons of course, but it's worthwhile when comparing it to other classes.

I'd drop the need for the saving throw altogether and change the damage to a bonus 1d10 poison damage on every hit, lasting 1 minute. This ups the average damage to 8 on every hit, with some good damage potential on a critical hit. I wouldn't put a 1d10 bonus on a Greatsword or Halberd, but on a dagger it's going to make it worth using.

 Oh should have stated it is a longsword, because they want it to be and most combat they already go into melee. I considered giving it the effect to also poison folks but wasn't sure if that was too much

With it being a long sword. I agree, make it just a d10 poison damage, maybe a bonus action, or just a free action to activate. Don't give it the poisoned condition. 

I think I will drop the con save because it does slow down combat and consider it for a later ability on a different item

I would avoid having it cost a bonus action as the Hexblade already has a lot of things to do with their bonus action.  

Here you go, I made it as a custom item for you.

https://www.dndbeyond.com/magic-items/3710210-hexvenom-longsword

Have you considered just using a Serpent's Fang. which is WOTC-canon?

Quote from quindraco >>

Have you considered just using a Serpent's Fang. which is WOTC-canon?

 

 Oh, yeah guess I can do that hahaha I feel silly now. Thank you