Skip to content

SLY - Candid Utility

SLY - Candid Utility

The SLY command line program tries to bundle a set of useful utility commands which can be used to improve the developer experience for anyone who wishes to create services on the top of the Internet Computer.

One area that we could improve was related to dealing with the Candid files. A candid file is used to describe the interface of a canister, and a client can use this interface in order to interact with the canister.

Developers can create the candid files for their canister either manually or automatically which is beside the subject of this chapter.

We understand that producing helpful diagnostic messages is crucial for a better developer experience, and that the lack of such error messages can cause frustration when you're already trying to solve complex problems. Since the official Candid parser by the DFINITY foundation was not producing concise and clear error messages, we forked it to create a custom version that captures and prints the diagnostic messages in a more helpful fashion. This new parser is used throughout Sly whenever you're dealing with a candid file.

Available Commands

The Candid related utility commands bundled in SLY, assume that you already have a candid file, and it helps you perform some common tasks on the files. This is the brief list of operations that we have (you can also run sly candid -h to see the list.)

  1. Check
  2. Format
  3. Gen


sly candid check <FILENAME>

This command can be used to verify the correctness of a candid file. It prints the diagnostic messages and exits with a non-zero exit code when an error is detected.

You can use this as part of your CI/CD pipeline if you manually maintain your candid files.


sly candid format [FILES]...

Pretty print a candid file, this command overwrites the original files, use with caution.


sly candid gen --js --ts --motoko --outdir ./bindings [FILES]...

Used to generate binding files in different languages for the provided candid files, it writes the generated files to the directory specified with --outdir/-o.