memorydetective

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Diagnose iOS retain cycles and performance regressions from your chat window. No Xcode required.

Highlights

• CLI-driven leak hunting. Read .memgraph files captured by Xcode (or by memorydetective itself on simulators), find ROOT CYCLEs, classify them against known SwiftUI/Combine patterns, and get a one-liner fix hint. All from a script or a chat.
• MCP-native. Plugs into Claude Code, Claude Desktop, Cursor, Cline, and any other MCP client. The agent drives the full investigate → classify → suggest-fix loop without you opening Instruments.
• Honest about its limits. No mocked outputs, no over-promises. Hangs analysis works clean from xctrace; sample-level Time Profile is parsed when xctrace symbolicates the trace and returns a structured workaround notice when it can't (the underlying xctrace SIGSEGV on heavy unsymbolicated traces is an Apple-side limitation we surface explicitly). Memory Graph capture works on Mac apps and iOS simulator; physical iOS devices still need Xcode.

What's new in v1.18 (2026-05-17): MetricKit + audit-close. analyzeMetricKitPayload is the 42nd MCP tool: ingests Apple MetricKit .mxdiagnostic JSON payloads from real-device TestFlight / App Store builds (post-mortem production diagnostics, no MCP competitor covers this lane today). Three actionable outputs: crash clusters by exception type / binary / top frame, hang hotspots with localized-duration parsing ("5.4 sec" / "20秒"), CPU + disk exceptions. Cross-tool chain hints (e.g. objc_release-style top frame surfaces a findCycles suggestion). Plus three audit-close items: open-enum SupportStatusKind (downstream consumers add kinds without a breaking type bump), invocation-scoped schemaDiscovery cache (summarizeTrace end-to-end shaved from ~28s to ~15s on real Apple traces via single up-front TOC fetch), and local-only integration tests against real Apple .trace bundles (closes the v1.14 P+O drift class for good). 701 → 757 tests. 41 → 42 MCP tools.

Also recent (v1.17): reliability pass. 14 bug fixes across three tiers. Headlines: strtobool env truthy parsing, verifyFix whitelist match modes (exact / substring / regex), recordViaInstrumentsApp catches traces saved outside watchDir, inspectTrace fault-tolerant fallback, configurable countAlive framework-noise filter, variable-size class min/max/median.

And v1.16: macOS 26.x recording-unblock release. New recordViaInstrumentsApp MCP tool wraps the Instruments.app GUI flow: opens the app, surfaces step-by-step instructions, watches a directory for the saved .trace, and chains into inspectTrace on success. Until Apple fixes the xcrun xctrace record regression on macOS 26.x sims, this is the automated path.

And v1.15: schema coverage + verify-fix UX. Three new MCP trace tools filled the remaining schema gap: analyzeMemoryFootprint (38th, VM resident / dirty / virtual + jetsam diagnosis), analyzeEnergyImpact (39th, battery drain investigation), analyzeLeakTimeline (40th, xctrace's leaks instrument as a time series). summarizeTrace now chains analyzeNetworkActivity. replayScenario captures simulator screenshots per step.

Earlier: v1.14 trace-side reliability, analyzeNetworkActivity, unified supportStatus[], FLEX-inspired countAlive size view, MLeaksFinder + DebugSwift-inspired verifyFix whitelist. v1.13 shipped summarizeTrace + /summarize-trace MCP prompt. v1.12 completed reference-tree propagation. v1.11 added inspectTrace, diffMemgraphs reference-tree. v1.9 shipped analyzeAbandonedMemory, detectLeaksInXCTest, cleanupTraces, mainThreadViolations. Full notes in CHANGELOG.

Heads up for macOS 26.x users: Apple shipped a task_for_pid kernel regression on macOS 26.x that blocks leaks --outputGraph, heap, AND xctrace --template Allocations against iOS simulator processes regardless of MallocStackLogging. Even Xcode's "View Memory Graph Hierarchy" hits it unless Malloc Stack Logging is enabled in the scheme's Diagnostics tab. memorydetective surfaces this as a proactive platformAdvisory on the first capture-class tool call, plus a workaroundNotice with issue: "macos-26-task-for-pid-broken" if leaks is invoked. The most reliable workaround today is to target an iOS 18 simulator runtime (install via Xcode > Settings > Platforms > +iOS 18.x). Empirically validated in the notelet investigation 2026-05-12 where three independent CLI memory-introspection paths all failed before iOS 18 was identified as the working escape hatch. Set MEMORYDETECTIVE_SUPPRESS_PLATFORM_ADVISORY=1 to silence the notice once you have settled on a workaround.

Also on macOS 26.x: xctrace record is broken for simulator targets. Independent from the task_for_pid regression above, xcrun xctrace record --time-limit Ns against iOS simulator processes wedges past the time limit, eventually exits when killed, and the resulting .trace bundle is missing template metadata. xctrace export --toc then fails with Document Missing Template Error. Re-validated against Xcode 26.5 (build 17F42, xctrace 16.0) 2026-05-15: regression survives the update. This hits the entire xctrace-based ecosystem the same way (memorydetective.recordTimeProfile, XcodeTraceMCP, and naked xcrun xctrace record calls all fail identically). Workarounds: (1) use recordViaInstrumentsApp (v1.16, hardened in v1.17), which opens Instruments.app for you, prompts you to record + save the .trace, then chains into inspectTrace automatically once the bundle appears. v1.17 also catches saves outside the watch directory via an Instruments.app AppleScript document query, returning savedOutsideWatchDir: true plus the actual path; (2) record from an older macOS host with Xcode 26.0 if you have one; (3) record against a physical device (the regression appears to be simulator-specific). v1.17 added a viability probe on recordTimeProfile (bundleStatus: "wedged" when the on-disk bundle is the 52K stub) and on inspectTrace (returns ok: true with diagnosis text instead of throwing). USAGE.md > Troubleshooting has a step-by-step.

Quickstart

npm install -g memorydetective

Add to your MCP client config (Claude Code shown):

// ~/.claude/settings.json
{
  "mcpServers": {
    "memorydetective": { "command": "memorydetective" }
  }
}

Or use it directly from the command line:

memorydetective analyze   ~/Desktop/myapp.memgraph
memorydetective classify  ~/Desktop/myapp.memgraph

→ See Examples for chat-driven flows · API for the full tool reference · Configure for Claude Desktop / Cursor / Cline · USAGE.md for the full walkthrough including how fixes flow from diagnosis to your codebase.

Examples

Realistic chat snippets. The agent calls the MCP tools listed in API.

Diagnose a leak from a memgraph

You: I just exported a memory graph at ~/Desktop/example.memgraph. Something's leaking after I close a detail screen. What is it?

Claude: (calls analyzeMemgraph → classifyCycle) Found 4 ROOT CYCLE blocks across 60,436 leaks. The dominant one matches swiftui.tag-index-projection with high confidence. A closure attached via .tag() on a photo carousel ForEach is capturing self strongly through _viewModel.wrappedValue, which keeps DetailViewModel and the navigation coordinator alive after dismissal.

Suggested fix: replace [weak self] capture in the tap handler with a static helper, or weak-capture the view-model via [weak coord = self.coordinator]. Want me to find the exact file?

Verify a fix actually worked

You: I shipped the fix. Compare ~/Desktop/before.memgraph to ~/Desktop/after.memgraph and tell me whether DetailViewModel count dropped.

Claude: (calls diffMemgraphs → countAlive) DetailViewModel: 12 → 0 (delta -12). The swiftui.tag-index-projection cycle is gone. Total leak count fell from 60,436 to 55,576 (−4,860). Three other ROOT CYCLEs persist. They're SwiftUI internals, not your code.

Self-contained verify-fix loop (v1.8)

When leaks --outputGraph fails on macOS 26.x (Failed to get DYLD info for task), the cause is usually that the app was not launched with MallocStackLogging=1. The new orchestration tools handle this end to end without you wiring up xcodebuild + simctl + axe yourself.

You: Reproduce the leak in MyApp for me. Build, launch with the right env vars, repeat the photo carousel flow 5 times to amplify it, capture before, then I'll ship the fix and you capture after.

Claude: (calls bootAndLaunchForLeakInvestigation) Built + booted iPhone 15 (UDID ABCD-...). Launched MyApp (PID 49581) with MallocStackLogging=1. Bundle id com.example.MyApp.

(calls replayScenario with 5 taps on the carousel + back-button cycle, repeat 5) Executed 25 actions in 12.3s. No failures.

(calls captureScenarioState({label:"before"})) Wrote before.memgraph (63,201 leaks), before.png, before.ui.json. MallocStackLogging active, no workaroundNotice.

(you ship the fix and rebuild)

(calls bootAndLaunchForLeakInvestigation + replay + captureScenarioState({label:"after"}))

(calls diffMemgraphs → verifyFix) DetailViewModel: 15 → 0. swiftui.tag-index-projection PASS. Bytes freed: 28.4 MB.

Find the slow path on a real device

You: Profile DemoApp on my iPhone for 90 seconds and tell me where the hangs are.

Claude: (calls listTraceDevices → recordTimeProfile → analyzeHangs) Recorded ~/Desktop/run.trace (90s, attached to DemoApp on iPhone 17 Pro Max). Found 23 user-visible hangs (>500 ms each), longest 1.16 s, average 769 ms. Severe load. All on the main thread. Sample-level hotspots aren't symbolicated yet; open the trace in Instruments for that step (analyzeTimeProfile returns a structured workaround notice when xctrace can't symbolicate. See CHANGELOG known limits).

Analyze MetricKit payloads from real-user crashes (v1.18)

You: I have a folder of .mxdiagnostic files from the last 30 days of TestFlight at ~/Downloads/metrickit-may/. What's catching real users?

Claude: (calls analyzeMetricKitPayload({ payloadDir: "~/Downloads/metrickit-may/" })) 47 payloads, 2026-04-15 → 2026-05-15. Top: 18 crashes EXC_BAD_ACCESS clustered on the same top frame, all in builds 456 and 457 (clean on 458 + earlier). Pattern matches retain-cycle release; chain hint surfaces findCycles next.

Second: 5.4s hang on libsqlite3.dylib (3 samples). Pattern db-lock. If you reproduce locally, chain into analyzeHangs with includeStackClassification: true for the mainThreadViolations[] classifier.

No symbolicated frames in v1.18 (raw binaryUUID + offset shipped; dSYM lookup is a separate tool, future release). Localized hang strings handled: input was "5.4 sec", normalized to 5400ms; one diagnostic carried "20秒" (Japanese), normalized to 20000ms.

See USAGE.md § MetricKit production post-mortem for the full end-to-end including how to wire analyzeMetricKitPayload into a verify-fix loop across multiple TestFlight builds.

End-to-end: leak → file → fix suggestion

The full loop, from artifact to code edit. Combines memory-graph analysis with Swift source-bridging.

You: Tem um leak. Memgraph em ~/Desktop/example-leaks.memgraph. The cycle points at DetailViewModel. Find where it lives in the project ~/Development/myapp/ and suggest a fix.

Claude: (calls analyzeMemgraph → classifyCycle → reachableFromCycle) Found 4 ROOT CYCLE blocks. The dominant one matches swiftui.tag-index-projection with high confidence. reachableFromCycle confirms 4 DetailViewModel instances pinning ~1100 NSURLSessionConfigurations each. The VM is the culprit, the network stack is collateral.

(calls swiftSearchPattern to locate .tag( + onImageSliderTap patterns in ~/Development/myapp/Sources/) 1 match in MyApp/Views/MediaCarousel.swift:142.

(calls swiftGetSymbolDefinition({ symbolName: "DetailViewModel", projectRoot: "...", candidatePaths: ["MyApp/ViewModels/"] })) Declared at MyApp/ViewModels/DetailViewModel.swift:18. class DetailViewModel: ObservableObject.

(calls swiftFindSymbolReferences to scope the blast radius. 7 callsites)

Suggested fix at MediaCarousel.swift:142:

swift

Copy

// before
.tag(index)
.onImageSliderTap { index in
    self.viewModel.handlePhotoTap(at: index)
}

// after. Static helper + weak captures
.tag(index)
.onImageSliderTap { [weak vm = _viewModel.wrappedValue,
                     weak coord = self.coordinator] index in
    Self.handlePhotoTap(index: index, viewModel: vm, coordinator: coord)
}

Want me to apply this and verify with a fresh .memgraph?

What it saves you

The pitch in one sentence: memorydetective turns a 50-500 MB binary memgraph (or a 200 KB leaks(1) text dump) into a 2-5 KB structured summary your AI agent can actually reason about. That changes the economics of using an LLM for iOS perf investigation.

Tokens (when paired with an AI agent like Claude / Cursor / Cline)

A real-world retain-cycle investigation, run twice. Once with memorydetective, once with the agent reading the raw leaks(1) output directly:

Translates to roughly $0.40-$1.20 per investigation depending on the model (Claude Opus / Sonnet / Haiku). Compounds linearly with file size and investigation depth.

Developer time

The same investigation, measured by the developer:

Numbers are rounded from a single anonymized real investigation (a SwiftUI retain cycle over a tagged ForEach that pinned ~28 MB of network-stack state). Your mileage will vary with cycle complexity and codebase size.

When the win is marginal

Be honest about where this doesn't help much:

• Tiny memgraphs (a single cycle, < 50 KB raw): MCP overhead is roughly token-neutral vs. Raw read. The dev-time win still holds (no manual cycle parsing) but the token win shrinks.
• One-shot symbol lookups without a leak attached: just use grep, you don't need this.
• First-time investigations on a new codebase: the agent still needs orientation turns regardless of MCP. The compounding wins kick in on the second and later investigations once the agent has cached the project's shape.

The win compounds with (a) file size, (b) investigation depth (multi-turn), and (c) how many leaks you investigate per quarter. For a single dev fixing one leak per year, the value is mostly the dev-time saving. For a team running CI gates with verifyFix across every PR, the token + time savings stack across hundreds of runs.

Configure

The memorydetective binary speaks MCP over stdio. Point any MCP-compatible client at it.

// ~/.claude/settings.json (global) or .mcp.json (per-project)
{
  "mcpServers": {
    "memorydetective": { "command": "memorydetective" }
  }
}

// ~/Library/Application Support/Claude/claude_desktop_config.json
{
  "mcpServers": {
    "memorydetective": { "command": "memorydetective" }
  }
}

// ~/.cursor/mcp.json
{
  "mcpServers": {
    "memorydetective": { "command": "memorydetective" }
  }
}

// VS Code settings.json
{
  "cline.mcpServers": {
    "memorydetective": { "command": "memorydetective" }
  }
}

{
  "mcpServers": {
    "memorydetective": { "command": "memorydetective" }
  }
}

{
  "servers": {
    "memorydetective": {
      "type": "stdio",
      "command": "memorydetective"
    }
  }
}

Environment variables

Every boolean MEMORYDETECTIVE_* flag below accepts the strtobool truthy set (case-insensitive): 1 / true / t / yes / y / on (truthy) and 0 / false / f / no / n / off (falsy). Unrecognized values emit a one-time stderr warning per variable and fall back to the documented default. Pre-v1.17 the parser was 1-only, which caused silent no-ops when operators exported =true or =yes. The advisory warning is gated on MEMORYDETECTIVE_SUPPRESS_PLATFORM_ADVISORY.

API

42 MCP tools + 34 Resources + 7 Prompts, grouped by purpose. Tool descriptions are tagged with a category prefix ([mg.memory], [mg.trace], [mg.build], [mg.scenario], [mg.code], [mg.log], [mg.render], [mg.ci], [mg.discover], [ops], [meta]) so related tools are visible at a glance.

Many tools include a suggestedNextCalls field in their response. A typed list of { tool, args, why } entries pre-populated from the current result, so the orchestrating LLM can chain calls without re-reasoning. Start with getInvestigationPlaybook(kind) for the canonical sequence. Or just type /investigate-leak (one of the Prompts) in any client that exposes MCP slash commands.

The cycle classifier ships 36 named antipatterns spanning SwiftUI (including the Swift 6 / @Observable / SwiftData / NavigationStack era, plus the v1.9 swiftui.observable-write-on-every-render shape), Combine, Swift Concurrency (incl. AsyncSequence-on-self and the new Observations API), UIKit (Timer/CADisplayLink/UIGestureRecognizer/KVO/URLSession/WebKit/DispatchSource, plus the v1.9 uikit.viewcontroller-retained-after-pop shape), Core Animation, Core Data, Coordinator pattern, and the popular third-party libs RxSwift + Realm. Each pattern carries:

• a textual one-line fixHint
• a confidence tier (high / medium / low)
• a staticAnalysisHint pointing at the SwiftLint rule that complements the runtime evidence (or an explicit gap notice when no rule exists. Reinforces the differentiator: memorydetective sees what linters miss at parse time)
• a fixTemplate with concrete Swift before/after snippets (new in v1.7) the agent can adapt directly to the user's code via the SourceKit-LSP source-bridging tools

Read & analyze (14)

All 9 trace-side analyzers below accept an optional second argument AnalyzeTraceOptions (v1.18 D-02). When called by summarizeTrace (which runs schema discovery once up front), the cache is forwarded so the per-analyzer xctrace --toc calls are skipped. Direct callers leave the option unset and behavior is identical to v1.17.

Capture / record (4)

Verify-fix orchestration (3, v1.8)

These three tools combine into a single deterministic verify-fix loop: launch the app with MallocStackLogging=1 so leaks works, drive the UI to amplify the suspected leak, snapshot before, ship the fix, snapshot after, then diffMemgraphs.

Discover (3)

Synthesize (1)

Production diagnostics (1, v1.18)

Render (1)

Ops (1)

CI / test integration (3)

Add memorydetective to your CI in 5 minutes

detectLeaksInXCTest + outputHtmlPath are the building blocks for a per-PR leak gate. The job below runs the named unit-test scheme on every push and PR, uploads the HTML report as a workflow artifact, and fails when new ROOT CYCLEs appear outside the allowlist. Copy the file into .github/workflows/leaks.yml and adjust the workspace + scheme + test identifier:

name: leaks
on: [push, pull_request]
jobs:
  detect-leaks:
    runs-on: macos-14
    timeout-minutes: 30
    steps:
      - uses: actions/checkout@v4
      - run: sudo xcode-select -s /Applications/Xcode_15.4.app
      - run: npm install -g memorydetective
      - run: |
          xcrun simctl boot "iPhone 15" || true
          xcrun simctl bootstatus "iPhone 15" -b
      - run: |
          cat > leaks.json <<EOF
          {
            "workspace": "DemoApp.xcworkspace",
            "scheme": "DemoAppTests",
            "destination": "platform=iOS Simulator,name=iPhone 15,OS=18.0",
            "testCaseFilter": "DemoTests/LeakSensitiveCase",
            "outputHtmlPath": "${GITHUB_WORKSPACE}/leak-report.html",
            "allowlistPatterns": ["SwiftUI", "_TtC"]
          }
          EOF
          memorydetective tool detectLeaksInXCTest --input leaks.json
      - if: always()
        uses: actions/upload-artifact@v4
        with:
          name: leak-report
          path: leak-report.html
          retention-days: 14

The same file is in examples/ci/github-actions-leaks.yml if you want to copy it verbatim. Notes:

• Simulator runtime: pin to iOS 18 on macos-14 runners. The macOS 26.x kernel regression (task_for_pid) breaks leaks against iOS 26 sims; iOS 18 is the canonical escape hatch (see the Highlights callout above).
• Allowlist patterns: substrings matched against the leaking ROOT CYCLE's root class. Use them to mask known pre-existing leaks while you work the backlog. _TtC covers Swift mangled class prefixes that occasionally show up in SwiftUI internals.
• HTML artifact: the report is self-contained (inline CSS, no external assets), so PR-comment bots and reviewers can preview it directly from the artifact URL.
• Build cache: add actions/cache@v4 keyed on Package.resolved + *.xcconfig to skip build-for-testing rebuilds across runs. Then pass --skipBuild to the second invocation when chaining multiple detectLeaksInXCTest calls on the same job.

Swift source bridging (5)

Pair the memory-graph diagnosis with source-code lookups via SourceKit-LSP. Closes the loop "found this leak in the cycle → find the file/line in your project".

These tools require macOS + Xcode (full Xcode, not just Command Line Tools. xcrun sourcekit-lsp must be available). They start a sourcekit-lsp subprocess per project root and reuse it across calls; the subprocess shuts down after a 5-minute idle window.

Why captureMemgraph doesn't work on physical iOS devices: leaks(1) only attaches to processes running on the local Mac (which includes iOS simulators). Memory Graph capture from a real device goes through Xcode's debugger over USB/lockdownd. Different mechanism, no public CLI equivalent.

Resources (34)

The cycle-pattern catalog is also surfaced as MCP resources, browsable at memorydetective://patterns/{patternId}. Each resource is a markdown body with the pattern name, a longer description, and the fix hint. Use this to let an agent (or a human in a UI-aware MCP client) browse the catalog without burning a classifyCycle call.

memorydetective://patterns/swiftui.tag-index-projection
memorydetective://patterns/concurrency.async-sequence-on-self
memorydetective://patterns/webkit.wkscriptmessagehandler-bridge
memorydetective://patterns/swiftdata.modelcontext-actor-cycle
…

resources/list returns all 34 entries. resources/read resolves any memorydetective://patterns/{id} URI to its markdown body.

Prompts (7)

Investigation playbooks are exposed as MCP prompts (slash commands in clients that surface them, e.g. Claude Code).

Each prompt fills the canonical playbook's argument templates with the user-provided values, then hands the agent a ready-to-execute brief. Calls the same tools listed in Read & analyze. Prompts are an orchestration shortcut, not a separate engine.

CLI mode

The same binary is also a thin CLI for scripting and CI:

memorydetective analyze   <path-to-.memgraph>          # totals, ROOT CYCLEs, diagnosis
memorydetective classify  <path-to-.memgraph>          # match patterns + render fix hint
memorydetective tool      <toolName> --input <json>    # generic dispatcher for any MCP tool
memorydetective --help
memorydetective --version

When called with no arguments, the binary starts as an MCP server over stdio.

The tool subcommand dispatches to any registered MCP tool by name, reading inputs from a JSON file. Exit code is 0 when the tool returns ok && passed !== false, 1 otherwise, so it slots cleanly into CI gates. Currently supported tool names: detectLeaksInXCTest, detectLeaksInXCUITest (the CI recipe above uses this).

Requirements

• macOS with Xcode Command Line Tools (xcode-select --install)
• Node.js ≥ 20

Develop

git clone https://github.com/carloshpdoc/memorydetective
cd memorydetective
npm install
npm test                  # 758 unit tests
npm run build             # build → dist/
npm run dev               # tsx, stdio mode (dev mode)
./scripts/demo.sh         # full demo against a real .memgraph (set MEMGRAPH=path)

Contributing

Contributions are welcome. Bug reports, feature requests, new cycle patterns, all of it.

• Bugs / feature requests: open an issue.
• PRs: fork → branch → npm install → make changes → npm test (758 tests must stay green) → open a PR with a concise description of what changed and why.

Adding a cycle pattern to classifyCycle

classifyCycle ships with 36 built-in patterns covering SwiftUI (incl. Swift 6 / @Observable / SwiftData / NavigationStack / the v1.9 observable-write-on-every-render and viewcontroller-retained-after-pop shapes), Combine, Swift Concurrency (incl. AsyncSequence-on-self and Observations), UIKit (Timer / CADisplayLink / UIGestureRecognizer / KVO / URLSession / WebKit / DispatchSource), Core Animation, Core Data, the Coordinator pattern, RxSwift, and Realm. To add one:

1. Edit src/tools/classifyCycle.ts. Add an entry to PATTERNS with id, name, fixHint, and a match function.
2. Add a test in src/tools/readTools.test.ts that asserts the new pattern fires against a representative memgraph fixture.
3. Add a staticAnalysisHint entry in src/runtime/staticAnalysisHints.ts (the test in that file enforces 1:1 coverage with PATTERNS).
4. Add a fixTemplate entry in src/runtime/fixTemplates.ts (same 1:1 coverage guard).
5. Open a PR.

Support this project

If memorydetective saves you time, you can support continued development:

• ☕ Buy me a coffee
• 💖 Sponsor on GitHub

Every contribution helps keep this maintained and documented.

License

Apache 2.0. See LICENSE and NOTICE.

Permits commercial use, modification, distribution, patent use. Includes attribution clause via the NOTICE file.

Why "memorydetective"?

Hunting retain cycles in SwiftUI feels like detective work: you have a body (the leaked instance), a crime scene (the .memgraph), and a chain of suspects (the retain chain). The tool helps you read the evidence and name the killer. The brand follows the work.