Tokenize, tag, and analyze natural language text using Apple's NaturalLanguage framework and translate between languages with the Translation framework. Use when adding language identification, sentiment analysis, named entity recognition, part-of-speech tagging, text embeddings, or in-app translation to iOS/macOS/visionOS apps.
npx skills add https://github.com/dpearson2699/swift-ios-skills --skill natural-language
Analyze natural language text for tokenization, part-of-speech tagging, named
entity recognition, sentiment analysis, language identification, and word/sentence
embeddings. Translate text between languages with the Translation framework.
> This skill covers two related frameworks: NaturalLanguage (NLTokenizer, NLTagger, NLEmbedding) for on-device text analysis, and Translation (TranslationSession, LanguageAvailability) for language translation.
Scope boundary: Use this skill after you already have text. It owns
tokenization, language identification, POS/NER tagging, sentiment, embeddings,
custom NLModel classifiers/taggers, and in-app translation. Hand off OCR to
vision-framework, speech-to-text to speech-recognition, UI strings and
locale formatting to ios-localization, and generative summarization or Apple
Intelligence workflows to apple-on-device-ai.
Import NaturalLanguage for text analysis and Translation for language
translation. No special entitlements or capabilities are required for
NaturalLanguage. Translation has split availability: system translation
presentation is iOS 17.4+ / macOS 14.4+, while TranslationSession,
.translationTask(), LanguageAvailability, and batch translation require
iOS 18+ / macOS 15+.
Direct TranslationSession(installedSource:target:) is the non-UI option, but
only when the source and target languages are already installed on device.
import NaturalLanguage
import Translation
NaturalLanguage classes (NLTokenizer, NLTagger) are not thread-safe.
Use each instance from one thread or dispatch queue at a time.
Segment text into words, sentences, or paragraphs with NLTokenizer.
import NaturalLanguage
func tokenizeWords(in text: String) -> [String] {
let tokenizer = NLTokenizer(unit: .word)
tokenizer.string = text
let range = text.startIndex..<text.endIndex
return tokenizer.tokens(for: range).map { String(text[$0]) }
}
| Unit | Description |
|---|---|
| .word | Individual words |
| .sentence | Sentences |
| .paragraph | Paragraphs |
| .document | Entire document |
Use enumerateTokens(in:using:) to detect numeric or emoji tokens.
let tokenizer = NLTokenizer(unit: .word)
tokenizer.string = text
tokenizer.enumerateTokens(in: text.startIndex..<text.endIndex) { range, attributes in
if attributes.contains(.numeric) {
print("Number: \(text[range])")
}
return true // continue enumeration
}
Detect the dominant language of a string with NLLanguageRecognizer.
func detectLanguage(for text: String) -> NLLanguage? {
NLLanguageRecognizer.dominantLanguage(for: text)
}
// Multiple hypotheses with confidence scores
func languageHypotheses(for text: String, max: Int = 5) -> [NLLanguage: Double] {
let recognizer = NLLanguageRecognizer()
recognizer.processString(text)
return recognizer.languageHypotheses(withMaximum: max)
}
Constrain the recognizer to expected languages for better accuracy on short text.
let recognizer = NLLanguageRecognizer()
recognizer.languageConstraints = [.english, .french, .spanish]
recognizer.processString(text)
let detected = recognizer.dominantLanguage
Identify nouns, verbs, adjectives, and other lexical classes with NLTagger.
func tagPartsOfSpeech(in text: String) -> [(String, NLTag)] {
let tagger = NLTagger(tagSchemes: [.lexicalClass])
tagger.string = text
var results: [(String, NLTag)] = []
let range = text.startIndex..<text.endIndex
let options: NLTagger.Options = [.omitPunctuation, .omitWhitespace]
tagger.enumerateTags(in: range, unit: .word, scheme: .lexicalClass, options: options) { tag, tokenRange in
if let tag {
results.append((String(text[tokenRange]), tag))
}
return true
}
return results
}
| Scheme | Output |
|---|---|
| .lexicalClass | Part of speech (noun, verb, adjective) |
| .nameType | Named entity type (person, place, organization) |
| .nameTypeOrLexicalClass | Combined NER + POS |
| .lemma | Base form of a word |
| .language | Per-token language |
| .sentimentScore | Sentiment polarity score |
Extract people, places, and organizations.
func extractEntities(from text: String) -> [(String, NLTag)] {
let tagger = NLTagger(tagSchemes: [.nameType])
tagger.string = text
var entities: [(String, NLTag)] = []
let options: NLTagger.Options = [.omitPunctuation, .omitWhitespace, .joinNames]
tagger.enumerateTags(
in: text.startIndex..<text.endIndex,
unit: .word,
scheme: .nameType,
options: options
) { tag, tokenRange in
if let tag, tag != .other {
entities.append((String(text[tokenRange]), tag))
}
return true
}
return entities
}
// NLTag values: .personalName, .placeName, .organizationName
Score text sentiment from -1.0 (negative) to +1.0 (positive).
func sentimentScore(for text: String) -> Double? {
let tagger = NLTagger(tagSchemes: [.sentimentScore])
tagger.string = text
let (tag, _) = tagger.tag(
at: text.startIndex,
unit: .paragraph,
scheme: .sentimentScore
)
return tag.flatMap { Double($0.rawValue) }
}
Measure semantic similarity between words or sentences with NLEmbedding.
func wordSimilarity(_ word1: String, _ word2: String) -> Double? {
guard let embedding = NLEmbedding.wordEmbedding(for: .english) else { return nil }
return embedding.distance(between: word1, and: word2, distanceType: .cosine)
}
func findSimilarWords(to word: String, count: Int = 5) -> [(String, Double)] {
guard let embedding = NLEmbedding.wordEmbedding(for: .english) else { return [] }
return embedding.neighbors(for: word, maximumCount: count, distanceType: .cosine)
}
Sentence embeddings compare entire sentences.
func sentenceSimilarity(_ s1: String, _ s2: String) -> Double? {
guard let embedding = NLEmbedding.sentenceEmbedding(for: .english) else { return nil }
return embedding.distance(between: s1, and: s2, distanceType: .cosine)
}
Show the built-in translation UI with .translationPresentation().
import SwiftUI
import Translation
struct TranslatableView: View {
@State private var showTranslation = false
let text = "Hello, how are you?"
var body: some View {
Button { showTranslation = true } label: {
Text(text)
}
.buttonStyle(.plain)
.translationPresentation(
isPresented: $showTranslation,
text: text
)
}
}
Use .translationTask() for programmatic translations within a view context.
struct TranslatingView: View {
@State private var translatedText = ""
@State private var translationErrorMessage: String?
@State private var configuration: TranslationSession.Configuration?
var body: some View {
VStack {
Text(translatedText)
Button("Translate") {
configuration = .init(source: Locale.Language(identifier: "en"),
target: Locale.Language(identifier: "es"))
}
}
.translationTask(configuration) { session in
do {
let response = try await session.translate("Hello, world!")
await MainActor.run {
translatedText = response.targetText
translationErrorMessage = nil
}
} catch {
let message = error.localizedDescription
await MainActor.run {
translationErrorMessage = message
}
}
}
}
}
Translate multiple strings in a single session.
.translationTask(configuration) { session in
do {
let requests = texts.enumerated().map { index, text in
TranslationSession.Request(sourceText: text,
clientIdentifier: "\(index)")
}
let responses = try await session.translations(from: requests)
for response in responses {
print("\(response.sourceText) -> \(response.targetText)")
}
} catch {
// Handle cancellation, unsupported languages, or download refusal.
}
}
let availability = LanguageAvailability()
let status = await availability.status(
from: Locale.Language(identifier: "en"),
to: Locale.Language(identifier: "ja")
)
switch status {
case .installed: break // Ready to translate offline
case .supported: break // Needs download
case .unsupported: break // Language pair not available
}
These classes are not thread-safe and will produce incorrect results or crash.
// WRONG
let sharedTagger = NLTagger(tagSchemes: [.lexicalClass])
DispatchQueue.concurrentPerform(iterations: 10) { _ in
sharedTagger.string = someText // Data race
}
// CORRECT
await withTaskGroup(of: Void.self) { group in
for _ in 0..<10 {
group.addTask {
let tagger = NLTagger(tagSchemes: [.lexicalClass])
tagger.string = someText
// process...
}
}
}
NaturalLanguage provides built-in linguistic analysis. Use Core ML for custom
trained models. They complement each other via NLModel.
// WRONG: Trying to do NER with raw Core ML
let coreMLModel = try MLModel(contentsOf: modelURL)
// CORRECT: Use NLTagger for built-in NER
let tagger = NLTagger(tagSchemes: [.nameType])
// Or load a custom Core ML model via NLModel
let nlModel = try NLModel(mlModel: coreMLModel)
tagger.setModels([nlModel], forTagScheme: .nameType)
Not all languages have word or sentence embeddings available on device.
// WRONG: Force unwrap
let embedding = NLEmbedding.wordEmbedding(for: .japanese)!
// CORRECT: Handle nil
guard let embedding = NLEmbedding.wordEmbedding(for: .japanese) else {
// Embedding not available for this language
return
}
Creating and configuring a tagger is expensive. Reuse it for the same text.
// WRONG: New tagger per word
for word in words {
let tagger = NLTagger(tagSchemes: [.lexicalClass])
tagger.string = word
}
// CORRECT: Set string once, enumerate
let tagger = NLTagger(tagSchemes: [.lexicalClass])
tagger.string = fullText
tagger.enumerateTags(in: fullText.startIndex..<fullText.endIndex,
unit: .word, scheme: .lexicalClass, options: []) { tag, range in
return true
}
Language detection on short strings (under ~20 characters) is unreliable.
Set constraints or hints to improve accuracy.
// WRONG: Detect language of a single word
let lang = NLLanguageRecognizer.dominantLanguage(for: "chat") // French or English?
// CORRECT: Provide context
let recognizer = NLLanguageRecognizer()
recognizer.languageHints = [.english: 0.8, .french: 0.2]
recognizer.processString("chat")
NLTokenizer and NLTagger instances used from a single threadNLEmbedding availability checked before use (returns nil if unavailable)LanguageAvailability checked before attempting translation.translationTask() used within a SwiftUI view hierarchyclientIdentifier to match responses to requests.joinNames option used with NER to keep multi-word names togetherNLModel, not raw Core MLGenerate Hugging Face Hub (huggingface_hub) release notes from cached PR JSON files. Use when asked to draft release notes from PR files.
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Take dpearson2699/natural-language from the repository into ~/.claude/skills for personal
use, or into .claude/skills inside a project.
The agent identifies a skill by the name field in its header. Two skills with the
same name cannot sit side by side — one of them will be ignored.