If a form offers "CST" as a timezone, someone still has to decide what those three letters mean. Chicago and Shanghai can both use that abbreviation while their clocks differ by fourteen hours. IANA documents this ambiguity, so treating the abbreviation as a unique identifier loses information before the conversion starts.
The Time API lets you use an abbreviation to discover candidates. It does not choose a region on the person's behalf:
GET /time/zones?abbreviation=CST&details=true&at=2026-01-15T12:00:00Z
Parse-Version: 2.0.0
The filter matches the exact abbreviation, ignoring case, at the supplied instant. The response always includes a timezones array of matching identifiers. details=true adds zones rows with context for a picker, including countries, offset, abbreviation, and daylight saving flags.
Here are two matching rows from the zones array, shown as an excerpt with other rows and fields omitted:
{
"zones": [
{
"timezone": "America/Chicago",
"countries": ["US"],
"abbreviation": "CST",
"offset": "-06:00"
},
{
"timezone": "Asia/Shanghai",
"countries": ["CN"],
"abbreviation": "CST",
"offset": "+08:00"
}
]
}
Those identifiers are the values to retain after a person makes a selection. An interface can display "America/Chicago, US, UTC-06:00" while storing America/Chicago. Pass that selected identifier to the clock or conversion route, such as /time/America/Chicago. Keeping only CST would discard the choice you just asked them to make.
If you already know the relevant country, add country=US to narrow the discovery request. area and offset can narrow it further when that context is known. These are filters, so they can still leave several matches. Supported aliases may also appear as separate identifiers. Several rows do not necessarily represent several different current clock readings.
The date in the request matters too. Chicago uses CST at the January instant above, but its abbreviation is CDT at the same UTC hour in July. An abbreviation search describes the rules at an instant. When investigating a recorded event with a known timestamp, pass that instant rather than today's clock. A new local appointment still needs a region choice before its instant can be resolved. If at is omitted, the response uses one captured current instant for all rows.
Use abbreviation=CST for this task. The q parameter searches identifier tokens. q=CST is not a substitute for the abbreviation filter. A search with no matches returns an empty timezones array, not a guessed zone.
The response includes timezone_database_version, identifying the bundled rule edition used for the result. Retain that context when it matters to your records. The identifier preserves the person's selected region, while the abbreviation and offset describe its clock under those rules at the requested time.