Restrictive covenants are contractual limits on what someone may do after leaving.
The three kinds
Non-compete — bars working for a competitor or setting up in competition, usually for a period and within an area.
Non-solicitation — bars approaching the business's customers or staff. Narrower, and generally far more enforceable.
Confidentiality — bars using or disclosing the business's confidential information. The most reliable of the three and the one most worth having.
Enforceability is jurisdictional and moving
Some states restrict non-competes heavily or ban them for most employees; others enforce reasonable ones. The position has changed in several places in recent years and continues to.
A clause that is unenforceable where the business operates is not merely useless. Attempting to enforce one can itself create liability.
This is a question for an employment attorney in the relevant state, and a template found online is particularly unreliable here.
What tends to be enforceable where they are permitted
Narrow scope, short duration, limited geography, and a genuine business interest being protected — customer relationships, confidential pricing, trade secrets — rather than simply preventing competition.
A clause covering everything for years across a whole state is the kind most often struck down entirely rather than narrowed.
The practical alternative
Confidentiality and non-solicitation, which are more enforceable and address most of what the business actually fears.
And reducing dependence: a business where relationships and knowledge sit with one person is exposed regardless of what they signed — see key person risk.
Signing point
At offer, not after starting. A covenant introduced later without anything given in exchange is weaker and in some jurisdictions unenforceable.