I want to turn a string into the 0x byte format inside an entrypoint.

If I try to use sp.pack() the actual value I want gets prepended with pack instructions as detailed here

I'm looking for a runtime equivalent of sp.utils.bytes_of_string() (which can only be used at compile time) that does not prepend anything to the string.

Is it possible to do this inside an entrypoint with smartpy?

  • Are you sure you have to use strings in the first place? All operations on strings are also available on bytes. Jan 21 at 15:52
  • yes, the entrypoint accepts a normal ipfs cid in string representation, and prepends ipfs:// to the received string in-contract before persisting it as the pointer to the tokens metadata, so it need to turn into its hex representation to work
    – 0x10
    Jan 22 at 5:15

2 Answers 2


I struggled on this for a while but finally reached a solution.

It's a bit hacky, but you just have to remove the 6 bytes that sp.pack prepends onto the bytes you actually want with sp.slice before using them.

padding = 6
string_length = sp.len(params.meta) + padding + 1

packed_string = sp.slice(

You can use the utilities provided in this repository: tezos-sc-utils

It provides utilities to encode and decode strings.

Here is an example of it working in SmartPy IDE: https://smartpy.io/ide?cid=QmbNMohfAQQqnG98aL1Rj3y5Y4KBJ7Vo9pWuMBfsCHy9mX&k=5ec3179b99a5aab6609e

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