Imported from thiennc-tesoglobal/ios-skills (skills/metrickit/SKILL.md). Install upstream with npx skills add thiennc-tesoglobal/ios-skills --skill metrickit. Copyright stays with the author.

MetricKit

Use MetricKit for low-overhead production telemetry that complements local Instruments and Xcode Organizer analysis. On iOS and iPadOS 27, prefer the Swift-first MetricManager report sequences. Keep MXMetricManager only in an explicit iOS 26 compatibility branch.

Beta-sensitive: The iOS/iPadOS 27 surface below is based on Apple's current beta documentation. It has not been locally compiler-verified because Xcode 27 is unavailable in this environment. Re-check the linked Apple documentation and compile with the shipping Xcode 27 SDK before release.

Load MetricKit Extended and Compatibility Patterns when implementing durable ingestion, detailed report analysis, or the iOS 26 compatibility path.

Contents

• MetricManager Setup
• Receiving Metric Reports
• Receiving Diagnostic Reports
• Key Metric Results
• Call Stack Trees
• Custom Signpost Metrics
• Durable Export and Upload
• Extended Launch Measurement
• iOS 26 Compatibility
• Xcode Organizer
• Scope Boundaries
• Common Mistakes
• Review Checklist
• References

MetricManager Setup

At app launch, create and retain one long-lived MetricManager. Start exactly one consumer task for metricReports and one for diagnosticReports.

Both properties expose nonthrowing AsyncSequence values:

• metricReports: some AsyncSequence<MetricReport, Never>
• diagnosticReports: some AsyncSequence<DiagnosticReport, Never>

Apple documents that concurrent consumers of one sequence can receive nondeterministic subsets. Fan out only after the single consumer receives and durably stores a report; delayed subscription can miss reports.

import MetricKit

@available(iOS 27.0, *)
final class MetricsService {
    private let manager = MetricManager()
    private var metricTask: Task<Void, Never>?
    private var diagnosticTask: Task<Void, Never>?

    func start(
        persistMetric: @escaping @Sendable (MetricReport) async -> Void,
        persistDiagnostic: @escaping @Sendable (DiagnosticReport) async -> Void
    ) {
        guard metricTask == nil, diagnosticTask == nil else { return }
        let manager = manager

        metricTask = Task {
            for await report in manager.metricReports {
                await persistMetric(report)
            }
        }

        diagnosticTask = Task {
            for await report in manager.diagnosticReports {
                await persistDiagnostic(report)
            }
        }
    }

    deinit {
        metricTask?.cancel()
        diagnosticTask?.cancel()
    }
}

The persistence closures are application-specific. Implement them with the durable-first workflow below rather than dropping, logging only, or directly uploading each report. If state-scoped metrics are needed, construct the manager with the documented init(enabledStateReportingDomains:) initializer and the required domains.

Receiving Metric Reports

MetricReport is Codable and Sendable. It describes an interval through:

• timeRange: DateInterval
• optional environment metadata
• intervalEntries for full-day and shorter interval measurements
• stateEntries for measurements associated with application states

Metric reports normally arrive on a daily cadence. Persist the complete report before extracting individual results.

For daily analysis, read the documented fullDayEntry and switch over its MetricResult values:

let entry = report.intervalEntries.fullDayEntry

for result in entry.values {
    switch result {
    case .hangTime(let metric):
        analyzeHangTime(metric)
    case .peakMemory(let metric):
        analyzePeakMemory(metric)
    case .timeToFirstDraw(let metric):
        analyzeLaunch(metric)
    case .signpostInterval(let metric):
        analyzeSignpost(metric)
    @unknown default:
        preserveUnknownMetric(result)
    }
}

Use @unknown default so a beta or future result does not make the ingestion pipeline brittle. Preserve the raw encoded report even when the current app does not understand a result.

Receiving Diagnostic Reports

DiagnosticReport is Codable and Sendable. It contains a timeRange, required environment metadata, and one DiagnosticResult.

Diagnostics are individual, event-based reports intended for prompt delivery when MetricKit produces them. Do not assume every crash, hang, or resource event generates a report; system sampling and eligibility still apply.

After durable storage, route the result explicitly:

switch report.result {
case .crash(let diagnostic):
    analyzeCrash(diagnostic)
case .hang(let diagnostic):
    analyzeHang(diagnostic)
case .cpuException(let diagnostic):
    analyzeCPUException(diagnostic)
case .diskWriteException(let diagnostic):
    analyzeDiskWrites(diagnostic)
case .appLaunch(let diagnostic):
    analyzeLaunch(diagnostic)
case .memoryException(let diagnostic):
    analyzeMemory(diagnostic)
@unknown default:
    preserveUnknownDiagnostic(report)
}

The iOS/iPadOS 27 diagnostic types are CrashDiagnostic, HangDiagnostic, CPUExceptionDiagnostic, DiskWriteExceptionDiagnostic, AppLaunchDiagnostic, and MemoryExceptionDiagnostic. The memory-exception case is new in iOS 27.

Useful fields include:

Key Metric Results

Choose a small telemetry vocabulary that matches the investigation rather than exporting every result. Prioritize the relevant categories: responsiveness and terminations; runtime, CPU, memory, network, and storage; or launch, display/GPU, and custom intervals.

Aggregate by app version and environment metadata, compare distributions rather than single values, and correlate regressions with releases. Avoid treating a daily aggregate as a precise trace of one user action.

Load the Key Metric Result Catalog when mapping exact MetricResult cases into a parser or dashboard.

Call Stack Trees

The iOS 27 CallStackTree replaces MXCallStackTree. It is Codable and Sendable and exposes:

• forEachFrame for frame traversal
• callStackThreads for thread-oriented analysis
• binaryInfo for image and binary metadata

Store the complete diagnostic report before flattening or symbolication. Preserve binary identifiers and offsets so server-side symbolication can use matching archives and dSYMs.

Custom Signpost Metrics

Create an OS log through the manager, then use mxSignpost for begin/end measurement:

let log = manager.logHandle(category: "ImagePipeline")

mxSignpost(.begin, log: log, name: "Decode")
await decodeImage()
mxSignpost(.end, log: log, name: "Decode")

MetricKit exposes the aggregate as MetricResult.signpostInterval. Do not search for a signpostMetrics array on MetricReport.

Use mxSignpost when MetricKit resource measurement is required. Apple documents that intervals created with OSSignposter and a MetricKit log handle do not populate the resource-measurement fields that mxSignpost provides.

Keep high-volume local tracing separate from the small set of stable production intervals used for MetricKit aggregation.

Durable Export and Upload

Treat report delivery as an at-least-once ingestion problem:

1. Encode the complete MetricReport or DiagnosticReport with JSONEncoder.
2. Atomically enqueue the bytes in an app-owned durable outbox.
3. Record report type, schema version, app version, and a stable deduplication key.
4. Acknowledge local processing only after the enqueue succeeds.
5. Upload later with retry, backoff, batching, and retention limits.
6. Mark the outbox item uploaded only after the server accepts it.

let data = try JSONEncoder().encode(report)
try await durableOutbox.enqueue(data, kind: .metric)

durableOutbox is an application-owned abstraction, not a MetricKit API. Do not perform a synchronous network upload inside the sequence consumer.

Durable local storage is the recovery mechanism for reports received through the modern sequences; do not make successful ingestion depend on an assumed modern backfill API.

Extended Launch Measurement

Use trackLaunchTask(id:onTrackingError:_:) on the manager for work that extends beyond time to first draw:

await manager.trackLaunchTask(
    id: "bootstrap-data",
    onTrackingError: { error in
        recordLaunchTrackingError(error)
    }
) {
    await bootstrapApplication()
}

The API is @MainActor and has synchronous and asynchronous overloads. The task closure's result and thrown error propagate to the caller; a MetricManager.LaunchTaskError is reported through onTrackingError without interrupting the tracked work. Results appear as MetricResult.extendedLaunch.

Use stable LaunchTaskID values and track only launch-critical work.

iOS 26 Compatibility

For an app that still deploys to iOS 26, use an availability boundary:

• iOS/iPadOS 27: use MetricManager and consume both async report sequences.
• iOS/iPadOS 26 and earlier supported releases: use MXMetricManager.shared, an MXMetricManagerSubscriber, and the legacy payload callbacks.

The legacy APIs remain the only documented branch with pastPayloads and pastDiagnosticPayloads. MXMetricManager is deprecated in iOS 27, so isolate it behind availability checks rather than mixing legacy payloads into the modern pipeline.

Load iOS 26 Compatibility for the full subscriber, legacy signpost, past-payload, and extended-launch patterns.

Xcode Organizer

Use Xcode Organizer to inspect Apple-aggregated production metrics, hangs, crashes, and regressions before building a custom backend. Use direct MetricKit ingestion when the product needs custom correlation, retention, alerting, or integration with an existing observability system.

Do not expect development-device runs to reproduce the population, cadence, or aggregation of production reports.

Scope Boundaries

MetricKit identifies production symptoms and trends. Route the actual code fix to the skill that owns the affected subsystem.

Common Mistakes

Review Checklist

• The iOS 27 branch starts at launch with one retained MetricManager and one consumer per report sequence.
• Every report is encoded and durably enqueued before analysis or upload.
• Diagnostic and metric switches use @unknown default.
• Unknown raw reports remain recoverable.
• Symbolication metadata and matching dSYMs are retained.
• Custom intervals use manager.logHandle(category:) and mxSignpost.
• Extended launch work uses trackLaunchTask.
• The iOS 26 MXMetricManager path is isolated behind availability checks.
• Production aggregates lead to a local Instruments investigation when appropriate.
• iOS 27 beta APIs have been rechecked and compiled with the shipping Xcode 27 SDK.

References

• MetricManager
• Metric report sequence
• Diagnostic report sequence
• MetricReport
• DiagnosticReport
• MetricResult
• DiagnosticResult
• CallStackTree
• Monitoring app performance with MetricKit
• Analyzing app performance with MetricKit
• iOS & iPadOS 27 release notes
• What's new in MetricKit (WWDC26)
• MetricKit Extended and Compatibility Patterns