diff --git a/Sources/SstData/DictionaryStore.swift b/Sources/SstData/DictionaryStore.swift
new file mode 100644
index 0000000..20072c1
--- /dev/null
+++ b/Sources/SstData/DictionaryStore.swift
@@ -0,0 +1,116 @@
+import Foundation
+import SstCore
+
+/// Owns `dictionary.txt`: reads, writes atomically, and notices edits made in another editor.
+@MainActor
+public final class DictionaryStore {
+    public static let header = """
+    # Sst woordenboek
+    # Eén invoer per regel. Een los woord is een term (voorrang bij het model).
+    # 'gehoord => schrijf' is een correctie, bijvoorbeeld: cloud code => Claude Code
+
+    """
+
+    public let fileURL: URL
+    public private(set) var file = DictionaryFile()
+    public var onChange: (() -> Void)?
+
+    private var lastText = ""
+    private var watcher: DispatchSourceFileSystemObject?
+    private var debounce: Task<Void, Never>?
+
+    public init(fileURL: URL) {
+        self.fileURL = fileURL
+    }
+
+    public var entries: [DictionaryEntry] { file.entries }
+
+    /// Reads the file; creates it with a short header when it does not exist yet.
+    public func load() throws {
+        try FileManager.default.createDirectory(
+            at: fileURL.deletingLastPathComponent(), withIntermediateDirectories: true)
+        if !FileManager.default.fileExists(atPath: fileURL.path) {
+            try Self.header.write(to: fileURL, atomically: true, encoding: .utf8)
+        }
+        let text = try String(contentsOf: fileURL, encoding: .utf8)
+        lastText = text
+        file = DictionaryFile(parsing: text)
+        onChange?()
+    }
+
+    /// Applies an edit and writes the file straight away.
+    public func apply(_ mutate: (inout DictionaryFile) -> Void) throws {
+        var updated = file
+        mutate(&updated)
+        let text = updated.serialized()
+        try text.write(to: fileURL, atomically: true, encoding: .utf8)
+        file = updated
+        lastText = text
+        onChange?()
+    }
+
+    /// Re-reads the file when its text differs from what we last wrote or read.
+    public func reloadIfChanged() {
+        guard let text = try? String(contentsOf: fileURL, encoding: .utf8), text != lastText else { return }
+        lastText = text
+        file = DictionaryFile(parsing: text)
+        onChange?()
+    }
+
+    /// Watches the folder (editors replace files instead of editing them in place).
+    public func startWatching() {
+        guard watcher == nil else { return }
+        let descriptor = open(fileURL.deletingLastPathComponent().path, O_EVTONLY)
+        guard descriptor >= 0 else { return }
+        let source = DispatchSource.makeFileSystemObjectSource(
+            fileDescriptor: descriptor, eventMask: .write, queue: .main)
+        source.setEventHandler { [weak self] in
+            MainActor.assumeIsolated { self?.scheduleReload() }
+        }
+        source.setCancelHandler { close(descriptor) }
+        source.resume()
+        watcher = source
+    }
+
+    public func stopWatching() {
+        watcher?.cancel()
+        watcher = nil
+        debounce?.cancel()
+    }
+
+    private func scheduleReload() {
+        debounce?.cancel()
+        debounce = Task { [weak self] in
+            try? await Task.sleep(for: .milliseconds(200))
+            guard !Task.isCancelled else { return }
+            self?.reloadIfChanged()
+        }
+    }
+}
+
+/// Bridges the dictionary to the controller: thread-safe, can be switched off, rebuilt when the dictionary changes.
+public final class DictionaryCorrector: TextCorrecting, @unchecked Sendable {
+    private let lock = NSLock()
+    private let knowledge: WordKnowledge
+    private var engine: CorrectionEngine
+    private var enabled = true
+
+    public init(knowledge: WordKnowledge) {
+        self.knowledge = knowledge
+        self.engine = CorrectionEngine(entries: [], knowledge: knowledge)
+    }
+
+    public func update(entries: [DictionaryEntry]) {
+        let rebuilt = CorrectionEngine(entries: entries, knowledge: knowledge)
+        lock.withLock { engine = rebuilt }
+    }
+
+    public func setEnabled(_ value: Bool) {
+        lock.withLock { enabled = value }
+    }
+
+    public func correct(_ text: String) -> CorrectionResult {
+        let (current, isOn) = lock.withLock { (engine, enabled) }
+        return isOn ? current.correct(text) : CorrectionResult(text: text, corrections: [])
+    }
+}
diff --git a/Tests/SstDataTests/DictionaryStoreTests.swift b/Tests/SstDataTests/DictionaryStoreTests.swift
new file mode 100644
index 0000000..f614813
--- /dev/null
+++ b/Tests/SstDataTests/DictionaryStoreTests.swift
@@ -0,0 +1,82 @@
+import Foundation
+import Testing
+import SstCore
+@testable import SstData
+
+@MainActor
+struct DictionaryStoreTests {
+    func tempFile() -> URL {
+        FileManager.default.temporaryDirectory.appending(path: "sst-tests-\(UUID().uuidString)/dictionary.txt")
+    }
+
+    @Test func loadCreatesAFileWithAHeaderWhenMissing() throws {
+        let url = tempFile()
+        let store = DictionaryStore(fileURL: url)
+        try store.load()
+        #expect(FileManager.default.fileExists(atPath: url.path))
+        #expect(store.entries.isEmpty)
+        #expect(try String(contentsOf: url, encoding: .utf8).hasPrefix("# Sst woordenboek"))
+    }
+
+    @Test func applyWritesAtomicallyAndKeepsComments() throws {
+        let url = tempFile()
+        let store = DictionaryStore(fileURL: url)
+        try store.load()
+        try store.apply { $0.append(.correction(heard: "cloud code", wrote: "Claude Code")) }
+        let text = try String(contentsOf: url, encoding: .utf8)
+        #expect(text.hasPrefix("# Sst woordenboek"))
+        #expect(text.hasSuffix("cloud code => Claude Code\n"))
+        #expect(store.entries == [pair("cloud code", "Claude Code")])
+    }
+
+    @Test func externalEditIsPickedUp() throws {
+        let url = tempFile()
+        let store = DictionaryStore(fileURL: url)
+        try store.load()
+        var changes = 0
+        store.onChange = { changes += 1 }
+        try "Vercel\n".write(to: url, atomically: true, encoding: .utf8)
+        store.reloadIfChanged()
+        #expect(store.entries == [term("Vercel")])
+        #expect(changes == 1)
+        store.reloadIfChanged()           // unchanged text: no second notification
+        #expect(changes == 1)
+    }
+
+    @Test func ourOwnWriteDoesNotTriggerAReload() throws {
+        let store = DictionaryStore(fileURL: tempFile())
+        try store.load()
+        try store.apply { $0.append(.term("Supabase")) }
+        var changes = 0
+        store.onChange = { changes += 1 }
+        store.reloadIfChanged()
+        #expect(changes == 0)
+    }
+
+    @Test func watcherNoticesAnEditorSavingTheFile() async throws {
+        let url = tempFile()
+        let store = DictionaryStore(fileURL: url)
+        try store.load()
+        var changed = false
+        store.onChange = { changed = true }
+        store.startWatching()
+        try "Anthropic\n".write(to: url, atomically: true, encoding: .utf8)
+        for _ in 0..<40 where !changed { try await Task.sleep(for: .milliseconds(100)) }
+        store.stopWatching()
+        #expect(changed)
+        #expect(store.entries == [term("Anthropic")])
+    }
+}
+
+struct DictionaryCorrectorTests {
+    @Test func correctsWhenEnabledAndPassesThroughWhenDisabled() {
+        let corrector = DictionaryCorrector(knowledge: FakeKnowledge())
+        corrector.update(entries: [pair("cloud code", "Claude Code")])
+        #expect(corrector.correct("cloud code").text == "Claude Code")
+        corrector.setEnabled(false)
+        #expect(corrector.correct("cloud code").text == "cloud code")
+        corrector.setEnabled(true)
+        corrector.update(entries: [])
+        #expect(corrector.correct("cloud code").text == "cloud code")
+    }
+}