
James G. answered 05/25/19
Former PMP Certified IT Project Manager
IEEE and ACM both have many templates available for doing this, particularly for IT, of which I can speak.
If it is for IT, I can offer some suggestions for content areas of a technical spec:
Title, Author, and Date
Design description_______________________________________________
Business Reason________________________________________________
Technical environment____________________________________________
File Name(s) or Database Name(s)__________________________________
Timing and Conditions for execution of program________________________
Data Volumes___________________________________________________
Risks and Issues with possiible mitigations_____________________________
Inputs including screen definitions____________________________________
Processing Logic with pseudocode and diagrams________________________
Outputs_________________________________________________________
Controls_________________________________________________________
Error Processing__________________________________________________
Data Mapping____________________________________________________
Dependencies/Related Processes including diagrams_____________________
Initial Test Strategy and Overview Plans