You can use Client Side code in Sage CRM workflow. The image below shows an Opportunity that is being progressed through a workflow in Sage CRM 7.3 sp3. In this example opportunity workflow the maximum certainty allowed for any stage has been controlled. e.g.
Lead - 5
Qualified - 10
Quote Submitted - 15
Negotiating - 20
The next image shows how in a workflow rule a individual rule action (in this case a 'Set Column Value' action) can have a script.
In this example the certainty field has a rule defined that looks like this:
if (this.value >10)
this.value = 10;
crm.infoMessage('Maximum value of certainty at this stage is 10');
If you wish to get other code into the workflow rule screen for clientside work you can use the workflow action 'Display Message on Screen' and use a translation to call a script: