.NET timezone
Resolve timezone IDs, conversions, scheduling, and persistence for .NET applications by selecting the right library, mapping Windows and IANA identifiers, and returning concise C# code that is safe across daylight saving time and platforms.
When to invoke
- "What timezone should I use for this city in .NET?"
- "Convert UTC to local time with TimeZoneInfo."
- "Make this timezone code work on Windows and Linux."
- "Handle daylight saving time in a C# scheduler."
- "Should I use DateTimeOffset or NodaTime?"
Prerequisites and context
- Read
references/timezone-index.md for common Windows and IANA mappings.
- Read
references/code-patterns.md for ready-to-use .NET timezone patterns.
- Default to
TimeZoneConverter for cross-platform Windows/IANA compatibility when the target runtime is unclear.
- Prefer
NodaTime for recurring schedules, strict timezone arithmetic, and DST-sensitive workflows.
Request routing
| Request type |
Recommended path |
| Address or location lookup |
Resolve geography to IANA zone, map to Windows ID, then return both IDs and offset/DST notes. |
| Timezone ID lookup |
Use references/timezone-index.md; always provide Windows and IANA formats. |
| UTC/local conversion |
Use TimeZoneInfo for platform-specific IDs or TimeZoneConverter for cross-platform IDs. |
| Cross-platform compatibility |
Use TZConvert.GetTimeZoneInfo(...) from TimeZoneConverter. |
| Scheduling or DST handling |
Use NodaTime and explicitly handle ambiguous and invalid local times. |
| API or persistence design |
Store instants in UTC and use DateTimeOffset for data transfer; persist a timezone ID when future local scheduling matters. |
Location resolution output
For every address, city, region, country, or place name, return this block and then a C# snippet.
Location: <resolved place>
Windows ID: <windows id>
IANA ID: <iana id>
UTC offset: <standard offset and DST offset when relevant>
DST: <yes/no>
If multiple locations are present, include one block per location and a combined multi-timezone snippet. If a location is ambiguous, list possible timezone matches and ask the user to choose.
Code patterns
| Pattern |
Use when |
Core API |
TimeZoneInfo |
Windows-only code or known platform-specific ID. |
TimeZoneInfo.FindSystemTimeZoneById(), TimeZoneInfo.ConvertTimeFromUtc(...). |
TimeZoneConverter |
Cross-platform conversion across Windows, Linux, containers, and Azure. |
TZConvert.GetTimeZoneInfo("Asia/Colombo"). |
NodaTime |
Recurring schedules, strict arithmetic, DST-sensitive jobs. |
DateTimeZone, Instant, ZonedDateTime, resolvers for skipped/repeated local times. |
DateTimeOffset |
APIs and data transfer where offset must travel with the value. |
DateTimeOffset and UTC normalization. |
| ASP.NET Core persistence/presentation |
Store UTC instants and display in user-selected zone. |
Database UTC column plus user timezone ID. |
| Recurring jobs and schedulers |
Future local time must stay local after DST changes. |
Store local schedule + zone ID, compute next occurrence with timezone rules. |
| Ambiguous and invalid DST timestamps |
Local time may repeat or not exist. |
Validate with TimeZoneInfo.IsAmbiguousTime() and TimeZoneInfo.IsInvalidTime() or NodaTime resolvers. |
using TimeZoneConverter;
TimeZoneInfo tz = TZConvert.GetTimeZoneInfo("Asia/Colombo");
DateTime local = TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, tz);
Pitfall warnings
| Pitfall |
Corrective rule |
TimeZoneInfo.FindSystemTimeZoneById() is platform-specific |
Use Windows IDs on Windows, IANA IDs on Linux/containers, or TimeZoneConverter to bridge both. |
Storing DateTime.Now in databases |
Store UTC instants; convert only at boundaries and presentation. |
DateTimeKind.Unspecified leaks into conversions |
Treat it as a bug risk unless it deliberately represents user-entered local wall time. |
| DST transitions skip or repeat local times |
Validate invalid and ambiguous local timestamps before scheduling or converting. |
| Azure Windows and Azure Linux differ |
Use the ID format expected by the host OS or use TimeZoneConverter. |
Keep answers production-safe, code-first, and explicit about third-party package requirements.
Output template
## .NET timezone result
**Status:** resolved | ambiguous | blocked
**Recommended approach:** <TimeZoneInfo | TimeZoneConverter | NodaTime | DateTimeOffset>
| Location or scenario | Windows ID | IANA ID | Offset/DST | Notes |
| --- | --- | --- | --- | --- |
| `<place or code path>` | `<windows>` | `<iana>` | `<offsets>` | `<pitfall>` |
<copy-paste-ready C# snippet>
**Package requirement:** `<none | TimeZoneConverter | NodaTime>`
**Warning:** <relevant pitfall>
Quality gate
Progressive disclosure and bundled resources
references/timezone-index.md: common Windows and IANA timezone mappings.references/code-patterns.md: ready-to-use .NET timezone patterns.
1---2name: dotnet-timezone3description: Resolve .NET and C# timezone questions with TimeZoneInfo, DateTimeOffset, TimeZoneConverter, NodaTime, UTC conversion, daylight saving time, scheduling, Windows and IANA timezone IDs, location lookup, and copy-paste-ready code. Use this skill when a .NET user needs the timezone for a city, address, region, or country, or asks about cross-platform timezone handling.4---56<!-- Generated from harness/github-copilot/skills/dotnet-timezone/SKILL.md by harness/claude-code/scripts/convert_from_copilot.py. Edit the source, not this file. -->78# .NET timezone910Resolve timezone IDs, conversions, scheduling, and persistence for .NET applications by selecting the right library, mapping Windows and IANA identifiers, and returning concise C# code that is safe across daylight saving time and platforms.1112## When to invoke1314- "What timezone should I use for this city in .NET?"15- "Convert UTC to local time with TimeZoneInfo."16- "Make this timezone code work on Windows and Linux."17- "Handle daylight saving time in a C# scheduler."18- "Should I use DateTimeOffset or NodaTime?"1920## Prerequisites and context2122- Read `references/timezone-index.md` for common Windows and IANA mappings.23- Read `references/code-patterns.md` for ready-to-use .NET timezone patterns.24- Default to `TimeZoneConverter` for cross-platform Windows/IANA compatibility when the target runtime is unclear.25- Prefer `NodaTime` for recurring schedules, strict timezone arithmetic, and DST-sensitive workflows.2627## Request routing2829| Request type | Recommended path |30| --- | --- |31| Address or location lookup | Resolve geography to IANA zone, map to Windows ID, then return both IDs and offset/DST notes. |32| Timezone ID lookup | Use `references/timezone-index.md`; always provide Windows and IANA formats. |33| UTC/local conversion | Use `TimeZoneInfo` for platform-specific IDs or `TimeZoneConverter` for cross-platform IDs. |34| Cross-platform compatibility | Use `TZConvert.GetTimeZoneInfo(...)` from `TimeZoneConverter`. |35| Scheduling or DST handling | Use `NodaTime` and explicitly handle ambiguous and invalid local times. |36| API or persistence design | Store instants in UTC and use `DateTimeOffset` for data transfer; persist a timezone ID when future local scheduling matters. |3738## Location resolution output3940For every address, city, region, country, or place name, return this block and then a C# snippet.4142```text43Location: <resolved place>44Windows ID: <windows id>45IANA ID: <iana id>46UTC offset: <standard offset and DST offset when relevant>47DST: <yes/no>48```4950If multiple locations are present, include one block per location and a combined multi-timezone snippet. If a location is ambiguous, list possible timezone matches and ask the user to choose.5152## Code patterns5354| Pattern | Use when | Core API |55| --- | --- | --- |56| `TimeZoneInfo` | Windows-only code or known platform-specific ID. | `TimeZoneInfo.FindSystemTimeZoneById()`, `TimeZoneInfo.ConvertTimeFromUtc(...)`. |57| `TimeZoneConverter` | Cross-platform conversion across Windows, Linux, containers, and Azure. | `TZConvert.GetTimeZoneInfo("Asia/Colombo")`. |58| `NodaTime` | Recurring schedules, strict arithmetic, DST-sensitive jobs. | `DateTimeZone`, `Instant`, `ZonedDateTime`, resolvers for skipped/repeated local times. |59| `DateTimeOffset` | APIs and data transfer where offset must travel with the value. | `DateTimeOffset` and UTC normalization. |60| ASP.NET Core persistence/presentation | Store UTC instants and display in user-selected zone. | Database UTC column plus user timezone ID. |61| Recurring jobs and schedulers | Future local time must stay local after DST changes. | Store local schedule + zone ID, compute next occurrence with timezone rules. |62| Ambiguous and invalid DST timestamps | Local time may repeat or not exist. | Validate with `TimeZoneInfo.IsAmbiguousTime()` and `TimeZoneInfo.IsInvalidTime()` or NodaTime resolvers. |6364```csharp65using TimeZoneConverter;6667TimeZoneInfo tz = TZConvert.GetTimeZoneInfo("Asia/Colombo");68DateTime local = TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, tz);69```7071## Pitfall warnings7273| Pitfall | Corrective rule |74| --- | --- |75| `TimeZoneInfo.FindSystemTimeZoneById()` is platform-specific | Use Windows IDs on Windows, IANA IDs on Linux/containers, or `TimeZoneConverter` to bridge both. |76| Storing `DateTime.Now` in databases | Store UTC instants; convert only at boundaries and presentation. |77| `DateTimeKind.Unspecified` leaks into conversions | Treat it as a bug risk unless it deliberately represents user-entered local wall time. |78| DST transitions skip or repeat local times | Validate invalid and ambiguous local timestamps before scheduling or converting. |79| Azure Windows and Azure Linux differ | Use the ID format expected by the host OS or use `TimeZoneConverter`. |8081Keep answers production-safe, code-first, and explicit about third-party package requirements.8283## Output template8485```markdown86## .NET timezone result8788**Status:** resolved | ambiguous | blocked89**Recommended approach:** <TimeZoneInfo | TimeZoneConverter | NodaTime | DateTimeOffset>9091| Location or scenario | Windows ID | IANA ID | Offset/DST | Notes |92| --- | --- | --- | --- | --- |93| `<place or code path>` | `<windows>` | `<iana>` | `<offsets>` | `<pitfall>` |9495 <copy-paste-ready C# snippet>9697**Package requirement:** `<none | TimeZoneConverter | NodaTime>`98**Warning:** <relevant pitfall>99```100101## Quality gate102103- [ ] The request type was identified before choosing a library.104- [ ] Location requests include Windows ID, IANA ID, UTC offset, and DST status for each resolved place.105- [ ] Cross-platform code uses `TimeZoneConverter` unless the platform-specific ID requirement is explicit.106- [ ] Recurring schedules or strict DST logic use or recommend `NodaTime`.107- [ ] API and persistence guidance stores UTC and preserves timezone IDs when future local scheduling matters.108- [ ] The response includes a minimal copy-paste-ready C# snippet and package guidance.109- [ ] Ambiguous locations or DST timestamps are not silently guessed.110111## Progressive disclosure and bundled resources112113- `references/timezone-index.md`: common Windows and IANA timezone mappings.114- `references/code-patterns.md`: ready-to-use .NET timezone patterns.
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