Question: Specifically [this](https://github.com/barrysteyn/node-scrypt). I know most bcrypt implementations are around 50 characters for, but I'm pretty certain that's not the case with scrypt.

Answer: 
From a developer of the successor of scrypt:

> 
> ...question that is related to both scrypt and yescrypt. Is there a maximum
>  input length for passwords?
> 
> 
> 

For the likely purposes of your question, no, there's no such length
limit. (Of course, in practice computers have limited memory and integer
variables in C have limited range, so there is some sort of large limit.)

I recommend that you do have some sane limit on the length of username
and password inputs in your web app anyway. Something that would never
get in the way of reasonable usage, but would prevent obviously
erroneous (maybe malicious) inputs from getting to deeper layers.

> 
> I know bcrypt has a limit of 71 characters.
> 
> 
> 

It's 72 for bcrypt.

Alexander
It should be noted that scrypt is *basically* `PBKDF2` for the bulk of it's work.

Basic use of PBKDF2 is:

```
bytes = PBKDF2(
      password, 
      salt, 
      numberOfBytes);

```

Scrypt is a glorified way of generating the salt fed to PBKDF2:

```
bytes = PBKDF2(
      password, 
      ScryptMixingStuff(password, originalSalt, N, r, p),
      numberOfBytes);

```

So the question becomes: What is the password length limitation in PBKDF2.

[There is no practical password length limitation of PBKDF2](https://crypto.stackexchange.com/questions/18765/maximum-password-length-in-pbkdf2). And so there is no practical password length limitation of scrypt.