---
title: Metadata Keys
framework: healthkit
role: collectionGroup
role_heading: API Collection
path: healthkit/metadata-keys
---

# Metadata Keys

Constants used to add metadata to objects stored in HealthKit.

## Overview

Overview Use these keys to facilitate sharing data between apps. You can also create your own custom keys to give HealthKit objects additional app-specific data.

## Topics

### General Keys

- [HKMetadataKeyExternalUUID](healthkit/hkmetadatakeyexternaluuid.md)
- [HKMetadataKeyTimeZone](healthkit/hkmetadatakeytimezone.md)
- [HKMetadataKeyWasUserEntered](healthkit/hkmetadatakeywasuserentered.md)
- [HKMetadataKeyQuantityClampedToLowerBound](healthkit/hkmetadatakeyquantityclampedtolowerbound.md)
- [HKMetadataKeyQuantityClampedToUpperBound](healthkit/hkmetadatakeyquantityclampedtoupperbound.md)

### Estimate Keys

- [HKMetadataKeyDateOfEarliestDataUsedForEstimate](healthkit/hkmetadatakeydateofearliestdatausedforestimate.md)
- [HKMetadataKeySessionEstimate](healthkit/hkmetadatakeysessionestimate.md)

### Device Information Keys

- [HKMetadataKeyDeviceSerialNumber](healthkit/hkmetadatakeydeviceserialnumber.md)
- [HKMetadataKeyUDIDeviceIdentifier](healthkit/hkmetadatakeyudideviceidentifier.md)
- [HKMetadataKeyUDIProductionIdentifier](healthkit/hkmetadatakeyudiproductionidentifier.md)
- [HKMetadataKeyDigitalSignature](healthkit/hkmetadatakeydigitalsignature.md)
- [HKMetadataKeyDeviceName](healthkit/hkmetadatakeydevicename.md)
- [HKMetadataKeyDeviceManufacturerName](healthkit/hkmetadatakeydevicemanufacturername.md)
- [HKMetadataKeyDevicePlacementSide](healthkit/hkmetadatakeydeviceplacementside.md)
- [HKDevicePlacementSide](healthkit/hkdeviceplacementside.md)
- [HKMetadataKeyAppleDeviceCalibrated](healthkit/hkmetadatakeyappledevicecalibrated.md)

### Sync Keys

- [HKMetadataKeySyncIdentifier](healthkit/hkmetadatakeysyncidentifier.md)
- [HKMetadataKeySyncVersion](healthkit/hkmetadatakeysyncversion.md)

### Lab Keys

- [HKMetadataKeyWasTakenInLab](healthkit/hkmetadatakeywastakeninlab.md)
- [HKMetadataKeyReferenceRangeLowerLimit](healthkit/hkmetadatakeyreferencerangelowerlimit.md)
- [HKMetadataKeyReferenceRangeUpperLimit](healthkit/hkmetadatakeyreferencerangeupperlimit.md)

### Weather Keys

- [HKMetadataKeyBarometricPressure](healthkit/hkmetadatakeybarometricpressure.md)
- [HKMetadataKeyWeatherCondition](healthkit/hkmetadatakeyweathercondition.md)
- [HKMetadataKeyWeatherHumidity](healthkit/hkmetadatakeyweatherhumidity.md)
- [HKMetadataKeyWeatherTemperature](healthkit/hkmetadatakeyweathertemperature.md)

### Workout Keys

- [Workout Metadata Keys](healthkit/workout-metadata-keys.md)

### Cardio Fitness Keys

- [HKMetadataKeyVO2MaxValue](healthkit/hkmetadatakeyvo2maxvalue.md)
- [HKMetadataKeyLowCardioFitnessEventThreshold](healthkit/hkmetadatakeylowcardiofitnesseventthreshold.md)

### Motion Keys

- [HKMetadataKeyUserMotionContext](healthkit/hkmetadatakeyusermotioncontext.md)

### Nutrition Keys

- [HKMetadataKeyFoodType](healthkit/hkmetadatakeyfoodtype.md)

### Vitals Sensors Keys

- [HKMetadataKeyBodyTemperatureSensorLocation](healthkit/hkmetadatakeybodytemperaturesensorlocation.md)
- [HKMetadataKeyHeartRateSensorLocation](healthkit/hkmetadatakeyheartratesensorlocation.md)
- [HKMetadataKeyHeartRateMotionContext](healthkit/hkmetadatakeyheartratemotioncontext.md)
- [HKPredicateKeyPathAverageHeartRate](healthkit/hkpredicatekeypathaverageheartrate.md)
- [HKMetadataKeyHeartRateRecoveryActivityDuration](healthkit/hkmetadatakeyheartraterecoveryactivityduration.md)
- [HKMetadataKeyHeartRateRecoveryActivityType](healthkit/hkmetadatakeyheartraterecoveryactivitytype.md)
- [HKMetadataKeyHeartRateRecoveryMaxObservedRecoveryHeartRate](healthkit/hkmetadatakeyheartraterecoverymaxobservedrecoveryheartrate.md)
- [HKMetadataKeyHeartRateRecoveryTestType](healthkit/hkmetadatakeyheartraterecoverytesttype.md)
- [HKMetadataKeyVO2MaxTestType](healthkit/hkmetadatakeyvo2maxtesttype.md)

### Audio Event Keys

- [HKMetadataKeyAudioExposureLevel](healthkit/hkmetadatakeyaudioexposurelevel.md)
- [HKMetadataKeyAudioExposureDuration](healthkit/hkmetadatakeyaudioexposureduration.md)
- [HKMetadataKeyHeadphoneGain](healthkit/hkmetadatakeyheadphonegain.md)

### Blood Glucose Keys

- [HKMetadataKeyBloodGlucoseMealTime](healthkit/hkmetadatakeybloodglucosemealtime.md)
- [HKMetadataKeyInsulinDeliveryReason](healthkit/hkmetadatakeyinsulindeliveryreason.md)

### Reproductive Health Keys

- [HKMetadataKeyMenstrualCycleStart](healthkit/hkmetadatakeymenstrualcyclestart.md)
- [HKMetadataKeySexualActivityProtectionUsed](healthkit/hkmetadatakeysexualactivityprotectionused.md)

### Algorithm Keys

- [HKMetadataKeyAlgorithmVersion](healthkit/hkmetadatakeyalgorithmversion.md)
- [HKMetadataKeyAppleECGAlgorithmVersion](healthkit/hkmetadatakeyappleecgalgorithmversion.md)
- [HKAppleECGAlgorithmVersion](healthkit/hkappleecgalgorithmversion.md)
- [HKPredicateKeyPathECGClassification](healthkit/hkpredicatekeypathecgclassification.md)
- [HKPredicateKeyPathECGSymptomsStatus](healthkit/hkpredicatekeypathecgsymptomsstatus.md)

## See Also

### Basic samples

- [HKCumulativeQuantitySample](healthkit/hkcumulativequantitysample.md)
- [HKDiscreteQuantitySample](healthkit/hkdiscretequantitysample.md)
- [HKQuantitySample](healthkit/hkquantitysample.md)
- [HKCategorySample](healthkit/hkcategorysample.md)
- [HKCorrelation](healthkit/hkcorrelation.md)
- [Units and quantities](healthkit/units-and-quantities.md)