How can I access custom blocks using Block.load(<slug>/<name>)?

I have defined a new custom block to connect to MongoDB as follows:

class MongoDBConnection(Block):
    host: str
    username: str
    password: SecretStr
    authSource: Optional[str] = 'admin'

    def get_client(self) -> MongoClient:
        return MongoClient(

I have registered the block using the cli as follows:

prefect block register --file

I have no issues using this block if I import the class from and call MongoDBConnection.load(<name>). However, I would like to use the generic Block.load(<slug>/<name>) pattern to avoid messy imports when sharing custom block definitions between flows.

I get the following error when I try to use the generic load pattern:

>>> mongo_block = Block.load('mongodbconnection/<name>')

KeyError: "No class found for dispatch key 'mongodbconnection' in registry for type 'Block'."

How would I go about using my custom blocks without needing messy imports?

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one option would be to install it as a package in your execution environment, as shown in the repo:

unfortunately, the flow code/module still must be installed within the environment, the block only stores the configuration data and methods server side, the code remains private on your infrastructure for privacy reasons

Fantastic, thank you! This is the solution I ended up using and it is very clean and simple.

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