Academic writing and web writing both use these constantly, often in the same document, which is where the trouble starts. You cite a source that lives on a site. Add "sight" — the third homophone, meaning vision — and you have three words with nothing in common but sound.
A verb. To quote or refer to a source as evidence or authority.
A noun. A place or location, physical or online. Occasionally a verb meaning to position something.
Cite, site and sight all sound exactly alike, so spelling has to do the work.
Cite is a verb meaning to quote or refer to something as evidence (cite your sources, cite a study), or to summon someone officially (he was cited for speeding). Site is a place: a building site, a campsite, a website. Sight is about seeing: eyesight, a sight worth seeing, love at first sight.
A good test is to ask what the word is doing. If someone is naming a source or being given an official notice, it is cite, and its noun is citation. If it is a location, real or online, it is site. If it has to do with the eyes or a view, it is sight.
Please site your sources at the end of the essay.
✓Please cite your sources at the end of the essay.
Naming a source as evidence is cite, the same root as citation.
Hard hats must be worn on the construction cite.
✓Hard hats must be worn on the construction site.
A place is a site.
The canyon at sunset was a beautiful site.
✓The canyon at sunset was a beautiful sight.
Something you look at is a sight.
Quick way to remember
Ask whether you are quoting or pointing. Quoting takes "cite," which shares its start with "citation." A place takes "site," which shares its start with "situated." And if the sentence is about eyes, it is "sight."
Is it "on-site" or "on sight"?
Both exist with different meanings. On-site means at the location (on-site parking). On sight means as soon as something is seen (recognized on sight).
Can I cite a website?
Yes, and it shows all three words at once: you cite (reference) a site (web location) that you have sighted (seen). Most citation styles include the page title, site name, date and URL.