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Version: 4.x

Contract Debugging

There are three ways to debug your ink! contract currently:

  • You can write tests using one of the mechanisms described on the Contract Testing page.
  • You can interact with your contract via a UI or command-line. This is described on the Call Your Contract page.
  • You can print debug statements in your contract. Those will appear on the Substrate node's stdout. This is described on this page.

How do I print to the terminal console from ink!?

You can use those two macros:

There are things you could do to enable debug messages on the client console:

  1. Enable the feature ink-debug for the ink_env crate.
    cargo-contract does this automatically for you (for versions >= 0.13.0), except if you compile a contract in --release mode.

  2. Set the log level of your node to runtime::contracts=debug.
    For example, to have only errors and debug output show up for the substrate-contracts-node:

    substrate-contracts-node -lerror,runtime::contracts=debug
  3. __Set the log level of your node to runtime::contracts::strace to trace host function calls. These function calls logs will also be displayed in the Debug message panel of Contracts UI. For example, to view these traces in addition to the logs described above:

    substrate-contracts-node -lerror,runtime::contracts=debug,runtime::contracts::strace=trace


The following code depicts how to print debug statements from a message or constructor.

fn new() -> Self {
ink::env::debug_println!("created new instance at {}", Self::env().block_number());
Self { }

fn print(&self) {
let caller = self.env().caller();
let message = ink_prelude::format!("got a call from {:?}", caller);

Debug output is not printed for transactions!

It is only printed for RPC calls or off-chain tests.