Expressions
Fill a node's field from the run's own data: the trigger, an earlier step's output, a secret or a function's result, worked out each time the node runs.
An expression is the part of a field between {{ and }}. Every function an expression can call is on Functions.
Write an expression
Fill a node's field from the run's data: pick a value in the Input pane, change it with a function, and see what the field holds before the flow runs.
What an expression can read
Every name an expression starts with, from json and node["Name"] to trigger and secret, and how to write the path to one field.
Dates, text and lists recipes
Ready-made expressions for the jobs flows do most: format a date, tidy up a name or an e-mail address, count a list or join it into one line.
When an expression fails
An expression shows a red message, or a run fails with EXPRESSION_ERROR. Find the message here, most likely first, and change the field to fix it.