Standard versus custom agent actions
Key Takeaway
You can change some standard actions by editing their underlying flow or prompt template, but adding or removing inputs or outputs takes a custom action that replaces the standard action.
Agent actions are the tools an Agentforce agent uses to get information or perform tasks. Salesforce provides standard actions for common Salesforce tasks. You create custom actions when your business needs something specific. A custom action points the agent at Salesforce functionality you build first, such as a flow, an Apex invocable method, or a prompt template.
What agent actions are
Actions are how an agent gets things done in Salesforce: the agent uses an action to get information or perform a task. Actions live inside subagents.
For example, imagine a user asks the agent for help writing an email. The agent can run an action that drafts and revises the email. That action grounds the email in relevant Salesforce data.