# Warnings (https://www.cal-sdk.com/docs/concepts/warnings)

Sometimes a provider can do most of what you asked but not all of it. Failing the whole call over an event color would be unhelpful, and dropping the color silently would be worse, so calsdk saves what it can and tells you what it couldn't. A warning means the call succeeded, but not exactly as asked. Every result has a `warnings` array:

```ts
const { event, warnings } = await createEvent({
  calendar, // microsoft(...)
  event: { title: 'Launch', start, end, color: '#d50000' },
});

console.log(warnings);
// [{ type: 'unsupported', feature: 'color', details: 'Outlook events have no color of their own. Use providerOptions.microsoft.categories instead.' }]
```

## Three types [#three-types]

| `type`          | Meaning                                                           | Fields                 |
| --------------- | ----------------------------------------------------------------- | ---------------------- |
| `unsupported`   | The provider ignored part of the request it cannot honor          | `feature`, `details?`  |
| `compatibility` | calsdk or the provider used a fallback that may behave a little differently | `feature`, `details?` |
| `other`         | Anything else worth knowing                                       | `message`              |

Some warnings you'll see:

- `compatibility` on `getFreeBusy` and `findFreeTime` for providers without a free/busy endpoint. Busy times were computed from events.
- `compatibility` on Google when a color is not one of its 11 event colors. The nearest one was saved.
- `unsupported` when `sendUpdates` asks for something a provider cannot do, such as Cal.com, which always emails attendees.
- `unsupported` for a `providerOptions` key the provider does not know.

## Where warnings go [#where-warnings-go]

Warnings are also logged, since it's easy to never look at a result's `warnings` array. Set `globalThis.CALSDK_WARNINGS` once, at startup, to choose where they go:

```ts
// Default: console.warn each distinct warning once per process.
globalThis.CALSDK_WARNINGS = 'console';

// Only return them on results.
globalThis.CALSDK_WARNINGS = 'silent';

// Send them somewhere else.
globalThis.CALSDK_WARNINGS = (warnings, { provider, operation }) => {
  logger.warn({ provider, operation, warnings }, 'calsdk warnings');
};
```

A function you set here runs for every call that has warnings. `iterateEvents` yields events, not results, so this setting is the only place its warnings reach.

## Warning or error? [#warning-or-error]

calsdk warns when the rest of the request still did what you asked. It throws `UnsupportedFunctionalityError` instead when going ahead would save a different schedule or lose data, such as a recurrence rule the provider cannot repeat. See [Errors](/docs/concepts/errors).