What is the actual skills gap?
Admins know: platform navigation, configuration, Update Sets, users/groups/roles, form design, basic workflows. Developers additionally know: Business Rule scripting, Script Includes, GlideAjax, API design, data modelling, scoped applications, REST integrations, performance optimisation.
The gap is scripting + design thinking. Everything else you already have.
Learn GlideRecord first
GlideRecord is the foundation of all ServiceNow scripting. Before anything else, become fluent in it. Write 50 different GlideRecord scripts on your PDI. Queries, inserts, updates, deletes, aggregates, encoded queries. This alone covers 30% of what developer interviews test.
Then Business Rules
Understand all four types (Before, After, Async, Display). Know when to use each. Write Business Rules that: set field values, create related records, prevent saves based on conditions, populate g_scratchpad for client use.
Then Client Scripts + GlideAjax
Understanding the client/server boundary — what runs where and how to move data between them — is the concept that separates developers from admins. Master GlideAjax. It is tested in every developer interview.
Build something real
The portfolio project that gets admins hired as developers: build a complete custom application. Not a tutorial — your own idea. An expense tracker, a vendor management system, a training request portal. It needs: custom tables, ACLs, Business Rules, a Service Catalog item, a report. You will refer to this in every interview.
Get the CAD certification
For many employers, moving from admin to developer without the CAD certification is a hard sell. It formally validates the development skills. Study for it after you have built your portfolio project — the exam topics will feel familiar.
How to position the transition in interviews
Do not downplay your admin experience. Frame it as: "I have N years of ServiceNow administration experience and have been developing on my PDI for the past X months, building [describe project]. I'm pursuing the CAD certification." This is actually a strong position — developers who understand administration are more valuable than pure developers who don't.