diff --git a/Sources/Loci/DocumentViewerView.swift b/Sources/Loci/DocumentViewerView.swift
index 88ffc20..71fdb90 100644
--- a/Sources/Loci/DocumentViewerView.swift
+++ b/Sources/Loci/DocumentViewerView.swift
@@ -8,6 +8,7 @@ enum DocumentViewerContent: Equatable {
     case image(URL)
     case quickLook(URL)
     case plainText(String)
+    case markdown(String)
     case websitePreview(thumbnailURL: URL?, websiteURL: URL?)
     case preparing(String)
     case unsupported(String)
@@ -85,6 +86,9 @@ enum DocumentViewerContentResolver {
            !DocumentPreviewConverter.isOfficeDocument(originalURL),
            let text = try? String(contentsOf: originalURL, encoding: .utf8),
            !text.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
+            if ext == "md" || ext == "markdown" {
+                return Result(content: .markdown(text), pdfPageCount: 0)
+            }
             return Result(content: .plainText(text), pdfPageCount: 0)
         }
 
diff --git a/Sources/Loci/ExtendDocumentViewer.swift b/Sources/Loci/ExtendDocumentViewer.swift
index 7af8286..8c79589 100644
--- a/Sources/Loci/ExtendDocumentViewer.swift
+++ b/Sources/Loci/ExtendDocumentViewer.swift
@@ -10,6 +10,9 @@ struct ExtendDocumentViewer: View {
     var item: ReferenceItem
     var originalURL: URL?
     @Binding var pageIndex: Int
+    /// Set when viewing a standalone file that is not in the library yet;
+    /// surfaces an "Add to Library" action in the toolbar.
+    var onAddToLibrary: (() -> Void)?
 
     @State private var content: DocumentViewerContent = .unsupported("Loading…")
     @State private var pageCount = 0
@@ -156,6 +159,7 @@ struct ExtendDocumentViewer: View {
                             .background(Color.white.opacity(0.08), in: RoundedRectangle(cornerRadius: 6, style: .continuous))
                     }
                     .menuStyle(.borderlessButton)
+                    .fixedSize()
                     viewerIconButton("plus") { adjustZoom(by: 10) }
                 }
             }
@@ -178,6 +182,17 @@ struct ExtendDocumentViewer: View {
                 .background(Color.white.opacity(0.10), in: RoundedRectangle(cornerRadius: 6, style: .continuous))
             }
 
+            if let onAddToLibrary {
+                Button("Add to Library", action: onAddToLibrary)
+                    .buttonStyle(.plain)
+                    .lociFont(size: 10, weight: .semibold, relativeTo: .caption2)
+                    .foregroundStyle(.white.opacity(0.82))
+                    .padding(.horizontal, 10)
+                    .padding(.vertical, 5)
+                    .background(Color.white.opacity(0.10), in: RoundedRectangle(cornerRadius: 6, style: .continuous))
+                    .help("Import a copy of this file into the Loci library")
+            }
+
             if let websiteURL = item.websiteURL, isWebsitePreview {
                 Button("Open in Browser") {
                     NSWorkspace.shared.open(websiteURL)
@@ -202,6 +217,7 @@ struct ExtendDocumentViewer: View {
                         .foregroundStyle(.white.opacity(0.55))
                 }
                 .menuStyle(.borderlessButton)
+                .fixedSize()
             }
         }
         .padding(.horizontal, 14)
@@ -247,6 +263,8 @@ struct ExtendDocumentViewer: View {
                 .frame(maxWidth: .infinity, maxHeight: .infinity)
         case .plainText(let text):
             ExtendTextCanvas(text: text)
+        case .markdown(let text):
+            ExtendMarkdownCanvas(text: text)
         case .websitePreview(let thumbnailURL, let websiteURL):
             ExtendWebsitePreviewCanvas(
                 item: item,
@@ -651,6 +669,183 @@ private struct ExtendTextCanvas: View {
     }
 }
 
+/// Renders markdown as formatted text on the dark viewer canvas. Block
+/// structure (headings, lists, quotes, fences) is parsed by hand because
+/// AttributedString's markdown init flattens it; inline emphasis, code, and
+/// links go through AttributedString. Obsidian-style [[wikilinks]] display as
+/// their titles — there is no vault context to resolve them against here.
+private struct ExtendMarkdownCanvas: View {
+    private enum Block {
+        case heading(level: Int, text: AttributedString)
+        case paragraph(AttributedString)
+        case listItem(marker: String, text: AttributedString, indent: Int)
+        case quote(AttributedString)
+        case code(String)
+        case rule
+    }
+
+    private let blocks: [Block]
+
+    init(text: String) {
+        blocks = Self.parse(text)
+    }
+
+    var body: some View {
+        ScrollView {
+            VStack(alignment: .leading, spacing: 10) {
+                ForEach(Array(blocks.enumerated()), id: \.offset) { _, block in
+                    blockView(block)
+                }
+            }
+            .frame(maxWidth: 720, alignment: .leading)
+            .frame(maxWidth: .infinity)
+            .padding(24)
+        }
+        .textSelection(.enabled)
+        .background(Color(red: 0.07, green: 0.07, blue: 0.08))
+    }
+
+    @ViewBuilder
+    private func blockView(_ block: Block) -> some View {
+        switch block {
+        case .heading(let level, let text):
+            Text(text)
+                .lociFont(
+                    size: [20, 17, 14.5, 13, 12.5, 12][min(level, 6) - 1],
+                    weight: .semibold,
+                    relativeTo: .headline
+                )
+                .foregroundStyle(.white.opacity(0.94))
+                .padding(.top, level <= 2 ? 8 : 4)
+        case .paragraph(let text):
+            Text(text)
+                .lociFont(size: 12.5, relativeTo: .body)
+                .lineSpacing(3.5)
+                .foregroundStyle(.white.opacity(0.82))
+        case .listItem(let marker, let text, let indent):
+            HStack(alignment: .firstTextBaseline, spacing: 8) {
+                Text(marker)
+                    .lociFont(size: 12, weight: .semibold, design: .rounded, relativeTo: .body)
+                    .foregroundStyle(.white.opacity(0.45))
+                Text(text)
+                    .lociFont(size: 12.5, relativeTo: .body)
+                    .lineSpacing(3)
+                    .foregroundStyle(.white.opacity(0.82))
+            }
+            .padding(.leading, CGFloat(indent) * 16)
+        case .quote(let text):
+            HStack(alignment: .top, spacing: 10) {
+                RoundedRectangle(cornerRadius: 1.5)
+                    .fill(Color.white.opacity(0.26))
+                    .frame(width: 3)
+                Text(text)
+                    .lociFont(size: 12.5, relativeTo: .body)
+                    .italic()
+                    .lineSpacing(3)
+                    .foregroundStyle(.white.opacity(0.64))
+            }
+            .fixedSize(horizontal: false, vertical: true)
+        case .code(let code):
+            Text(code)
+                .lociFont(size: 11, design: .monospaced, relativeTo: .caption)
+                .foregroundStyle(.white.opacity(0.80))
+                .frame(maxWidth: .infinity, alignment: .leading)
+                .padding(12)
+                .background(Color.white.opacity(0.06), in: RoundedRectangle(cornerRadius: 8, style: .continuous))
+        case .rule:
+            Rectangle()
+                .fill(Color.white.opacity(0.12))
+                .frame(height: 1)
+                .padding(.vertical, 4)
+        }
+    }
+
+    private static func parse(_ raw: String) -> [Block] {
+        var blocks: [Block] = []
+        var paragraph: [String] = []
+        var fenceLines: [String]?
+        var lines = raw.replacingOccurrences(of: "\r\n", with: "\n").components(separatedBy: "\n")[...]
+
+        // YAML frontmatter is metadata, not prose; show it as a code block.
+        if lines.first?.trimmingCharacters(in: .whitespaces) == "---",
+           let closing = lines.dropFirst().firstIndex(where: { $0.trimmingCharacters(in: .whitespaces) == "---" }) {
+            blocks.append(.code(lines[lines.startIndex + 1..<closing].joined(separator: "\n")))
+            lines = lines[(closing + 1)...]
+        }
+
+        func flushParagraph() {
+            guard !paragraph.isEmpty else { return }
+            blocks.append(.paragraph(inline(paragraph.joined(separator: " "))))
+            paragraph.removeAll()
+        }
+
+        for line in lines {
+            let trimmed = line.trimmingCharacters(in: .whitespaces)
+
+            if fenceLines != nil {
+                if trimmed.hasPrefix("```") {
+                    blocks.append(.code(fenceLines?.joined(separator: "\n") ?? ""))
+                    fenceLines = nil
+                } else {
+                    fenceLines?.append(line)
+                }
+                continue
+            }
+            if trimmed.hasPrefix("```") {
+                flushParagraph()
+                fenceLines = []
+                continue
+            }
+            if trimmed.isEmpty {
+                flushParagraph()
+                continue
+            }
+            if trimmed == "---" || trimmed == "***" || trimmed == "___" {
+                flushParagraph()
+                blocks.append(.rule)
+                continue
+            }
+            let hashes = trimmed.prefix(while: { $0 == "#" }).count
+            if (1...6).contains(hashes), trimmed.dropFirst(hashes).first == " " {
+                flushParagraph()
+                let content = trimmed.dropFirst(hashes).trimmingCharacters(in: .whitespaces)
+                blocks.append(.heading(level: hashes, text: inline(content)))
+                continue
+            }
+            if trimmed.hasPrefix(">") {
+                flushParagraph()
+                let content = trimmed.dropFirst().trimmingCharacters(in: .whitespaces)
+                blocks.append(.quote(inline(content)))
+                continue
+            }
+            let indent = line.prefix(while: { $0 == " " || $0 == "\t" }).reduce(0) { $0 + ($1 == "\t" ? 2 : 1) } / 2
+            if trimmed.hasPrefix("- ") || trimmed.hasPrefix("* ") || trimmed.hasPrefix("+ ") {
+                flushParagraph()
+                blocks.append(.listItem(marker: "•", text: inline(String(trimmed.dropFirst(2))), indent: indent))
+                continue
+            }
+            if let match = trimmed.firstMatch(of: /^(\d{1,3})\.\s+(.*)$/) {
+                flushParagraph()
+                blocks.append(.listItem(marker: "\(match.1).", text: inline(String(match.2)), indent: indent))
+                continue
+            }
+            paragraph.append(trimmed)
+        }
+        if let fenceLines {
+            blocks.append(.code(fenceLines.joined(separator: "\n")))
+        }
+        flushParagraph()
+        return blocks
+    }
+
+    private static func inline(_ text: String) -> AttributedString {
+        var normalized = text.replacing(/\[\[([^\]|]+)\|([^\]]+)\]\]/) { String($0.output.2) }
+        normalized = normalized.replacing(/\[\[([^\]]+)\]\]/) { String($0.output.1) }
+        let options = AttributedString.MarkdownParsingOptions(interpretedSyntax: .inlineOnlyPreservingWhitespace)
+        return (try? AttributedString(markdown: normalized, options: options)) ?? AttributedString(normalized)
+    }
+}
+
 private struct ExtendPreparingCanvas: View {
     var message: String
 
diff --git a/Sources/Loci/LociApp.swift b/Sources/Loci/LociApp.swift
index abdab99..346df35 100644
--- a/Sources/Loci/LociApp.swift
+++ b/Sources/Loci/LociApp.swift
@@ -23,6 +23,9 @@ extension Notification.Name {
 final class LociAppDelegate: NSObject, NSApplicationDelegate, NSWindowDelegate, NSToolbarDelegate {
     private var window: NSWindow?
     private var settingsWindow: NSWindow?
+    private var markdownWindows: [NSWindow] = []
+    /// Files handed to us before the main window finished launching.
+    private var pendingMarkdownURLs: [URL] = []
     private var localAPI: LocalReferenceAPIServer?
     private var libraryStore: LibraryStore?
 
@@ -74,6 +77,12 @@ final class LociAppDelegate: NSObject, NSApplicationDelegate, NSWindowDelegate,
         DispatchQueue.main.asyncAfter(deadline: .now() + 0.45) { [weak libraryStore] in
             libraryStore?.finishDeferredStartupWork()
         }
+
+        let queued = pendingMarkdownURLs
+        pendingMarkdownURLs.removeAll()
+        for url in queued {
+            openStandaloneMarkdown(url)
+        }
     }
 
     func applicationShouldTerminateAfterLastWindowClosed(_ sender: NSApplication) -> Bool {
@@ -81,18 +90,56 @@ final class LociAppDelegate: NSObject, NSApplicationDelegate, NSWindowDelegate,
     }
 
     func application(_ application: NSApplication, open urls: [URL]) {
-        for url in urls where url.scheme == "loci" {
-            Task {
-                do {
-                    try await XOAuthManager.shared.completeAuthorization(from: url)
-                    openSettings()
-                } catch {
-                    ErrorPresenter.shared.show(.networkError("X sign-in failed: \(error.localizedDescription)"))
+        for url in urls {
+            if url.scheme == "loci" {
+                Task {
+                    do {
+                        try await XOAuthManager.shared.completeAuthorization(from: url)
+                        openSettings()
+                    } catch {
+                        ErrorPresenter.shared.show(.networkError("X sign-in failed: \(error.localizedDescription)"))
+                    }
+                }
+            } else if url.isFileURL, ["md", "markdown"].contains(url.pathExtension.lowercased()) {
+                if window == nil {
+                    pendingMarkdownURLs.append(url)
+                } else {
+                    openStandaloneMarkdown(url)
                 }
             }
         }
     }
 
+    /// Opens a markdown file in its own viewer window, reading it in place —
+    /// no library import happens unless the user asks from the viewer.
+    private func openStandaloneMarkdown(_ url: URL) {
+        let viewer = StandaloneMarkdownViewer(fileURL: url, store: libraryStore)
+        let hostingController = NSHostingController(rootView: viewer)
+        let window = NSWindow(
+            contentRect: NSRect(x: 0, y: 0, width: 780, height: 660),
+            styleMask: [.titled, .closable, .miniaturizable, .resizable],
+            backing: .buffered,
+            defer: false
+        )
+        window.title = url.lastPathComponent
+        // The document viewer draws a dark canvas; give this window a dark
+        // titlebar (overriding the app-wide light pin) so the chrome matches.
+        window.appearance = NSAppearance(named: .darkAqua)
+        window.backgroundColor = NSColor(srgbRed: 0.07, green: 0.07, blue: 0.08, alpha: 1)
+        window.contentMinSize = NSSize(width: 480, height: 360)
+        window.contentViewController = hostingController
+        // NSHostingController shrinks the window to the SwiftUI ideal size
+        // (the frame minimums here); restore the intended reading size.
+        window.setContentSize(NSSize(width: 780, height: 660))
+        window.isReleasedWhenClosed = false
+        window.center()
+        window.makeKeyAndOrderFront(nil)
+        NSApp.activate(ignoringOtherApps: true)
+
+        markdownWindows.removeAll { !$0.isVisible && !$0.isMiniaturized }
+        markdownWindows.append(window)
+    }
+
     private func setupMenus() {
         let mainMenu = NSMenu()
         let appName = AppBrand.name
diff --git a/Sources/Loci/LociTelemetry.swift b/Sources/Loci/LociTelemetry.swift
index 6acb926..90bee6f 100644
--- a/Sources/Loci/LociTelemetry.swift
+++ b/Sources/Loci/LociTelemetry.swift
@@ -66,12 +66,17 @@ enum LociTelemetry {
         "x_bookmark_count"
     ]
 
+    /// Enabled by default; users opt out from Settings → Privacy. An explicit
+    /// choice under either the current or legacy key always wins.
     static var isEnabled: Bool {
         get {
             if UserDefaults.standard.object(forKey: enabledKey) != nil {
                 return UserDefaults.standard.bool(forKey: enabledKey)
             }
-            return UserDefaults.standard.bool(forKey: legacyEnabledKey)
+            if UserDefaults.standard.object(forKey: legacyEnabledKey) != nil {
+                return UserDefaults.standard.bool(forKey: legacyEnabledKey)
+            }
+            return true
         }
         set { UserDefaults.standard.set(newValue, forKey: enabledKey) }
     }
diff --git a/Sources/Loci/ScrollFeel.swift b/Sources/Loci/ScrollFeel.swift
index 998844a..eb4969e 100644
--- a/Sources/Loci/ScrollFeel.swift
+++ b/Sources/Loci/ScrollFeel.swift
@@ -24,6 +24,7 @@ struct LociScrollFeel: NSViewRepresentable {
 final class ScrollFeelProbeView: NSView {
     var profile: LociScrollFeel.Profile = .library
     private weak var configuredScrollView: NSScrollView?
+    private var retriesRemaining = 0
 
     override func viewDidMoveToSuperview() {
         super.viewDidMoveToSuperview()
@@ -40,14 +41,24 @@ final class ScrollFeelProbeView: NSView {
     }
 
     func scheduleConfiguration() {
+        retriesRemaining = 40
         DispatchQueue.main.async { [weak self] in
             self?.configureScrollView()
         }
     }
 
     private func configureScrollView() {
+        // Detached probes get a fresh viewDidMoveToWindow when they return to
+        // a hierarchy; retrying while detached would spin the main queue at
+        // 100% CPU forever, so both the window guard and the retry budget are
+        // load-bearing.
+        guard window != nil else { return }
         guard let scrollView = enclosingScrollView else {
-            scheduleConfiguration()
+            guard retriesRemaining > 0 else { return }
+            retriesRemaining -= 1
+            DispatchQueue.main.asyncAfter(deadline: .now() + 0.05) { [weak self] in
+                self?.configureScrollView()
+            }
             return
         }
 
diff --git a/Sources/Loci/SettingsView.swift b/Sources/Loci/SettingsView.swift
index f7a38e7..f46c658 100644
--- a/Sources/Loci/SettingsView.swift
+++ b/Sources/Loci/SettingsView.swift
@@ -44,7 +44,7 @@ struct SettingsView: View {
     @AppStorage("LociAutoCompile") private var autoCompile = false
     @AppStorage("LociVaultPath") private var vaultPath = ""
     @AppStorage("LociXRedirectMode") private var xRedirectModeRaw = XOAuthRedirectMode.recommended.rawValue
-    @AppStorage(LociTelemetry.enabledKey) private var telemetryEnabled = false
+    @AppStorage(LociTelemetry.enabledKey) private var telemetryEnabled = true
     @AppStorage(LociTelemetry.endpointKey) private var telemetryEndpoint = ""
 
     @StateObject private var xOAuth = XOAuthManager.shared
diff --git a/Sources/Loci/StandaloneMarkdownViewer.swift b/Sources/Loci/StandaloneMarkdownViewer.swift
new file mode 100644
index 0000000..7415a8c
--- /dev/null
+++ b/Sources/Loci/StandaloneMarkdownViewer.swift
@@ -0,0 +1,53 @@
+import AppKit
+import SwiftUI
+
+/// Viewer for markdown files opened from Finder ("Open With → Loci") or via
+/// drag onto the app icon. The file is read in place from wherever it lives on
+/// disk — nothing is copied into the library unless the user asks with the
+/// toolbar's Add to Library action.
+struct StandaloneMarkdownViewer: View {
+    let fileURL: URL
+    var store: LibraryStore?
+
+    @State private var itemID = UUID()
+    @State private var pageIndex = 0
+    @State private var addedToLibrary = false
+
+    private var item: ReferenceItem {
+        ReferenceItem(
+            id: itemID,
+            title: fileURL.deletingPathExtension().lastPathComponent,
+            subtitle: fileURL.deletingLastPathComponent().lastPathComponent,
+            fileName: fileURL.lastPathComponent,
+            kind: .typography,
+            group: .file,
+            theme: .paper,
+            aspectRatio: 0.77,
+            collectionID: nil,
+            isInbox: false,
+            isTrashed: false,
+            canvasPosition: .zero,
+            infinityPosition: .zero
+        )
+    }
+
+    var body: some View {
+        ExtendDocumentViewer(
+            item: item,
+            originalURL: fileURL,
+            pageIndex: $pageIndex,
+            onAddToLibrary: addToLibraryAction
+        )
+        .padding(10)
+        .frame(minWidth: 480, minHeight: 360)
+        .background(Color(red: 0.07, green: 0.07, blue: 0.08))
+    }
+
+    private var addToLibraryAction: (() -> Void)? {
+        guard let store, !addedToLibrary else { return nil }
+        return {
+            store.importFiles([fileURL])
+            addedToLibrary = true
+        }
+    }
+}
diff --git a/Support/Loci.Info.plist b/Support/Loci.Info.plist
index d7504e5..fc0f5da 100644
--- a/Support/Loci.Info.plist
+++ b/Support/Loci.Info.plist
@@ -18,6 +18,42 @@
     <string>Loci</string>
     <key>CFBundlePackageType</key>
     <string>APPL</string>
+    <key>CFBundleDocumentTypes</key>
+    <array>
+        <dict>
+            <key>CFBundleTypeName</key>
+            <string>Markdown Document</string>
+            <key>CFBundleTypeRole</key>
+            <string>Viewer</string>
+            <key>LSHandlerRank</key>
+            <string>Alternate</string>
+            <key>LSItemContentTypes</key>
+            <array>
+                <string>net.daringfireball.markdown</string>
+            </array>
+        </dict>
+    </array>
+    <key>UTImportedTypeDeclarations</key>
+    <array>
+        <dict>
+            <key>UTTypeIdentifier</key>
+            <string>net.daringfireball.markdown</string>
+            <key>UTTypeDescription</key>
+            <string>Markdown Document</string>
+            <key>UTTypeConformsTo</key>
+            <array>
+                <string>public.plain-text</string>
+            </array>
+            <key>UTTypeTagSpecification</key>
+            <dict>
+                <key>public.filename-extension</key>
+                <array>
+                    <string>md</string>
+                    <string>markdown</string>
+                </array>
+            </dict>
+        </dict>
+    </array>
     <key>CFBundleURLTypes</key>
     <array>
         <dict>
diff --git a/Tests/LociTests/TelemetryTests.swift b/Tests/LociTests/TelemetryTests.swift
index c834c63..d9ff3e2 100644
--- a/Tests/LociTests/TelemetryTests.swift
+++ b/Tests/LociTests/TelemetryTests.swift
@@ -4,10 +4,15 @@ import Testing
 
 @Suite("Telemetry")
 struct TelemetryTests {
-    @Test("Telemetry is opt-in and allowlisted")
-    func telemetryOptInAndAllowlist() async throws {
+    @Test("Telemetry defaults on, honors opt-out, and allowlists properties")
+    func telemetryDefaultAndAllowlist() async throws {
         LociTelemetry.clearLocalQueue()
         LociTelemetry.endpointString = ""
+
+        UserDefaults.standard.removeObject(forKey: LociTelemetry.enabledKey)
+        UserDefaults.standard.removeObject(forKey: "AtlasTelemetryEnabled")
+        #expect(LociTelemetry.isEnabled)
+
         LociTelemetry.isEnabled = false
 
         LociTelemetry.record(.importCompleted, properties: [