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npx skills add ...
Documentation
SKILL.md
npx skills add dpearson2699/swift-ios-skills --skill healthkit
Read, write, and query Apple Health data using HealthKit. Covers HKHealthStore authorization, sample queries, statistics queries, statistics collection queries for charts, saving HKQuantitySample data, background delivery, workout sessions with HKWorkoutSession and HKLiveWorkoutBuilder, HKUnit, and HKQuantityTypeIdentifier values. Use when integrating with Apple Health, displaying health metrics, recording workouts, or enabling background health data delivery.
npx skills add dpearson2699/swift-ios-skills --skill healthkit
Read and write health and fitness data from the Apple Health store. Covers authorization, queries, writing samples, background delivery, and workout sessions. Targets Swift 6.3 / iOS 26+.
NSHealthShareUsageDescription (read) and NSHealthUpdateUsageDescription (write) to Info.plistAlways check availability before calling other HealthKit APIs. Health data is available on iOS, watchOS, visionOS, iPadOS 17+, and iOS apps running on Vision Pro. It is unavailable on iPadOS 16 or earlier and may be restricted by managed device policy.
Create a single HKHealthStore instance and reuse it throughout your app. It
is thread-safe. If HealthKit is optional, review Xcode's generated
UIRequiredDeviceCapabilities healthkit entry so unsupported devices are not
excluded unintentionally.
Request only the types your app genuinely needs. App Review rejects apps that over-request.
authorizationStatus(for:) reports write/share authorization. HealthKit does
not reveal whether read permission was granted or denied. If the user denies
read access, queries return only samples your app successfully saved, which may
look like empty or partial data.
Use HKSampleQueryDescriptor (async/await) for one-shot reads. Prefer descriptors over the older callback-based HKSampleQuery.
Use HKStatisticsQueryDescriptor for aggregated single-value stats (sum, average, min, max).
Options by data type:
.cumulativeSum.discreteAverage, .discreteMin, .discreteMaxUse HKStatisticsCollectionQueryDescriptor for time-series data grouped into intervals -- ideal for charts.
Use results(for:) (plural) to get an AsyncSequence that emits updates as new data arrives:
Create HKQuantitySample objects and save them to the store.
Treat try await healthStore.save(sample) returning as the save success gate;
only then report success or advance app state. On failure, surface the error and
correct the known authorization, type, unit, duration, or input problem before
constructing another sample. A bounded query or inspection in the Health app is
useful as an integration-test check when persistence evidence is required, but
is not a mandatory production read after every save.
Your app can only delete samples it created. Samples from other apps or Apple Watch are read-only.
Register for background updates so your app is launched when new data arrives. Requires the background delivery entitlement.
Pair with an HKObserverQuery to handle notifications. Always call the completion handler:
Frequencies: .immediate, .hourly, .daily, .weekly
Set up observer queries as soon as the app launches, then call
enableBackgroundDelivery once for the same sample type. The system persists
the registration, wakes the app at most once per requested frequency, and
enforces tighter caps for some types such as hourly step-count delivery on iOS.
Background delivery is not supported on Simulator; test it on device.
Use HKWorkoutSession and HKLiveWorkoutBuilder to track live workouts.
HKWorkoutSession is available on iOS/iPadOS 17+, visionOS 1+, and watchOS 2+.
HKLiveWorkoutBuilder is available on iOS/iPadOS 26+ and watchOS 5+, so gate
live-builder code if supporting older iOS/iPadOS releases.
On iPhone and iPad, live heart-rate collection requires a paired external heart rate sensor. Apple Watch sessions can collect high-frequency heart-rate data. For locked iPhone workouts, plan for the system's workout-data access flow before showing health metrics on the Lock Screen.
Do not call endCollection and finishWorkout immediately after requesting the
stop. Wait for the session delegate's .stopped transition, then await
builder.endCollection(at:) followed by builder.finishWorkout(). Report the
workout as saved and clear session state only after both operations return.
Handle each thrown error without blindly repeating teardown. A successful
finishWorkout() can return no workout object while the device is locked, so a
nil result alone is not failure.
For full workout lifecycle management including pause/resume, delegate handling, and multi-device mirroring, see references/healthkit-patterns.md.
| Identifier | Category | Unit |
|---|---|---|
.stepCount | Fitness | .count() |
.distanceWalkingRunning | Fitness | .meter() |
.activeEnergyBurned | Fitness | .kilocalorie() |
.basalEnergyBurned | Fitness | .kilocalorie() |
.heartRate | Vitals | .count()/.minute() |
.restingHeartRate | Vitals | .count()/.minute() |
.oxygenSaturation | Vitals | .percent() |
.bodyMass | Body | .gramUnit(with: .kilo) |
.bodyMassIndex | Body | .count() |
.height | Body | .meter() |
.bodyFatPercentage | Body | .percent() |
.bloodGlucose | Lab | .gramUnit(with: .milli).unitDivided(by: .literUnit(with: .deci)) |
Common category types: .sleepAnalysis, .mindfulSession, .appleStandHour
Read-only user characteristics include .dateOfBirth, .biologicalSex,
.bloodType, .fitzpatrickSkinType, .wheelchairUse, and .activityMoveMode.
.sharingAuthorized before saving, but read denial is privacy-protected and
looks like app-owned-only, empty, or partial results.isHealthDataAvailable(). Check before HealthKit access and
handle unavailable or restricted stores without crashing..immediate means immediate. Background delivery is capped by
the system and must be tested on device.HKHealthStore.isHealthDataAvailable() checked before any HealthKit accessInfo.plist includes NSHealthShareUsageDescription and/or NSHealthUpdateUsageDescriptionHKHealthStore instance reused (not created per query)HKObserverQuery setup and
completionHandler calledenableBackgroundDelivery.stopped transition before
endCollection and finishWorkout; state clears only after successful
finalizationfunc requestAuthorization() async throws {
let typesToShare: Set<HKSampleType> = [
HKQuantityType(.stepCount),
HKQuantityType(.activeEnergyBurned)
]
let typesToRead: Set<HKObjectType> = [
HKQuantityType(.stepCount),
HKQuantityType(.heartRate),
HKQuantityType(.activeEnergyBurned),
HKCharacteristicType(.dateOfBirth)
]
try await healthStore.requestAuthorization(
toShare: typesToShare,
read: typesToRead
)
}let status = healthStore.authorizationStatus(
for: HKQuantityType(.stepCount)
)
switch status {
case .notDetermined:
// Haven't requested yet -- safe to call requestAuthorization
break
case .sharingAuthorized:
// User granted write access
break
case .sharingDenied:
// User denied write access (read denial is indistinguishable from "no data")
break
@unknown default:
break
}func fetchRecentHeartRates() async throws -> [HKQuantitySample] {
let heartRateType = HKQuantityType(.heartRate)
let descriptor = HKSampleQueryDescriptor(
predicates: [.quantitySample(type: heartRateType)],
sortDescriptors: [SortDescriptor(\.endDate, order: .reverse)],
limit: 20
)
let results = try await descriptor.result(for: healthStore)
return results
}
// Extracting values from samples:
for sample in results {
let bpm = sample.quantity.doubleValue(
for: HKUnit.count().unitDivided(by: .minute())
)
print("\(bpm) bpm at \(sample.endDate)")
}func fetchTodayStepCount() async throws -> Double? {
let calendar = Calendar.current
let startOfDay = calendar.startOfDay(for: Date())
let endOfDay = calendar.date(byAdding: .day, value: 1, to: startOfDay)!
let predicate = HKQuery.predicateForSamples(
withStart: startOfDay, end: endOfDay
)
let stepType = HKQuantityType(.stepCount)
let samplePredicate = HKSamplePredicate.quantitySample(
type: stepType, predicate: predicate
)
let query = HKStatisticsQueryDescriptor(
predicate: samplePredicate,
options: .cumulativeSum
)
let result = try await query.result(for: healthStore)
return result?.sumQuantity()?.doubleValue(for: .count())
}func fetchDailySteps(forLast days: Int) async throws -> [(date: Date, steps: Double)] {
let calendar = Calendar.current
let endDate = calendar.startOfDay(
for: calendar.date(byAdding: .day, value: 1, to: Date())!
)
let startDate = calendar.date(byAdding: .day, value: -days, to: endDate)!
let predicate = HKQuery.predicateForSamples(
withStart: startDate, end: endDate
)
let stepType = HKQuantityType(.stepCount)
let samplePredicate = HKSamplePredicate.quantitySample(
type: stepType, predicate: predicate
)
let query = HKStatisticsCollectionQueryDescriptor(
predicate: samplePredicate,
options: .cumulativeSum,
anchorDate: endDate,
intervalComponents: DateComponents(day: 1)
)
let collection = try await query.result(for: healthStore)
var dailySteps: [(date: Date, steps: Double)] = []
collection.statisticsCollection.enumerateStatistics(
from: startDate, to: endDate
) { statistics, _ in
let steps = statistics.sumQuantity()?
.doubleValue(for: .count()) ?? 0
dailySteps.append((date: statistics.startDate, steps: steps))
}
return dailySteps
}let updateStream = query.results(for: healthStore)
Task {
for try await result in updateStream {
// result.statisticsCollection contains updated data
}
}func saveSteps(count: Double, start: Date, end: Date) async throws {
let stepType = HKQuantityType(.stepCount)
let quantity = HKQuantity(unit: .count(), doubleValue: count)
let sample = HKQuantitySample(
type: stepType,
quantity: quantity,
start: start,
end: end
)
try await healthStore.save(sample)
}func enableStepCountBackgroundDelivery() async throws {
let stepType = HKQuantityType(.stepCount)
try await healthStore.enableBackgroundDelivery(
for: stepType,
frequency: .hourly
)
}let observerQuery = HKObserverQuery(
sampleType: HKQuantityType(.stepCount),
predicate: nil
) { query, completionHandler, error in
defer { completionHandler() } // Must call to signal done
guard error == nil else { return }
// Fetch new data, update UI, etc.
}
healthStore.execute(observerQuery)func startWorkout() async throws {
let configuration = HKWorkoutConfiguration()
configuration.activityType = .running
configuration.locationType = .outdoor
let session = try HKWorkoutSession(
healthStore: healthStore,
configuration: configuration
)
session.delegate = self
let builder = session.associatedWorkoutBuilder()
builder.dataSource = HKLiveWorkoutDataSource(
healthStore: healthStore,
workoutConfiguration: configuration
)
session.startActivity(with: Date())
try await builder.beginCollection(at: Date())
}
// Request teardown; finalize from the delegate's .stopped transition.
session.stopActivity(with: Date())// Basic units
HKUnit.count() // Steps, counts
HKUnit.meter() // Distance
HKUnit.mile() // Distance (imperial)
HKUnit.kilocalorie() // Energy
HKUnit.joule(with: .kilo) // Energy (SI)
HKUnit.gramUnit(with: .kilo) // Mass (kg)
HKUnit.pound() // Mass (imperial)
HKUnit.percent() // Percentage
// Compound units
HKUnit.count().unitDivided(by: .minute()) // Heart rate (bpm)
HKUnit.meter().unitDivided(by: .second()) // Speed (m/s)
// Prefixed units
HKUnit.gramUnit(with: .milli) // Milligrams
HKUnit.literUnit(with: .deci) // Deciliters