Comprehend

Protocol: JSON 1.1 (X-Amz-Target: Comprehend_20171127.*) Endpoint: POST http://localhost:4566/

Supported Actions

Action	Description
DetectSentiment	Detect the overall sentiment of a text (POSITIVE/NEGATIVE/NEUTRAL/MIXED)
DetectKeyPhrases	Detect key noun-phrases in a text
DetectDominantLanguage	Detect the dominant language of a text
DetectPiiEntities	Detect personally identifiable information (PII) in a text
ContainsPiiEntities	Report whether a text contains PII, without locating it

Emulation Behavior

• Stub responses: every action returns a fixed, AWS-shaped response — no real NLP/ML is performed. DetectSentiment always returns NEUTRAL, DetectKeyPhrases always returns one stub phrase, DetectDominantLanguage always reports en, and DetectPiiEntities/ContainsPiiEntities always report no PII found.
• Real input validation: Text and LanguageCode (where applicable) are still required and LanguageCode is validated against Comprehend's supported set — this is protocol compatibility, not content analysis. DetectSentiment and DetectKeyPhrases accept the general set (en, es, fr, de, it, pt, ar, hi, ja, ko, zh, zh-TW); DetectPiiEntities and ContainsPiiEntities accept only en/es, matching AWS's narrower support for PII detection.
• Out of scope: the async job/model-training surface (DocumentClassifier, EntityRecognizer, Flywheel, Dataset, Endpoint operations), DetectEntities, and DetectSyntax are not implemented.
• Intentional deviation: real Comprehend enforces a maximum input size on Text and returns TextSizeLimitExceededException when exceeded. This is not enforced here — any non-empty Text is accepted regardless of length.

Configuration

Variable	Default	Description
FLOCI_SERVICES_COMPREHEND_ENABLED	true	Enable or disable the service
AI_MOCK_CONFIG	unset	Path to a shared mock-response config file — see "Mock Responses" below

Mock Responses

The default stub responses above are the same for every call. To exercise application logic that branches on detection results (e.g. "escalate if sentiment is NEGATIVE"), point AI_MOCK_CONFIG at a JSON file shared across Comprehend, Textract, and Rekognition:

{
  "comprehend": {
    "I am furious about this outage": {
      "DetectSentiment": { "Sentiment": "NEGATIVE", "SentimentScore": { "Positive": 0.0, "Negative": 0.95, "Neutral": 0.05, "Mixed": 0.0 } }
    }
  }
}

The lookup key is the exact Text value sent in the request. The file is re-read when its modification time changes, so it can be edited without restarting the emulator. A missing file, an unset AI_MOCK_CONFIG, or no matching entry all fall back to the default stub — mocking is opt-in and never breaks a call that isn't using it.

Examples

export AWS_ENDPOINT_URL=http://localhost:4566

aws comprehend detect-sentiment \
  --text "Floci makes local AWS testing painless" \
  --language-code en \
  --endpoint-url $AWS_ENDPOINT_URL

aws comprehend detect-key-phrases \
  --text "Floci makes local AWS testing painless" \
  --language-code en \
  --endpoint-url $AWS_ENDPOINT_URL

aws comprehend detect-dominant-language \
  --text "Floci makes local AWS testing painless" \
  --endpoint-url $AWS_ENDPOINT_URL

aws comprehend detect-pii-entities \
  --text "My SSN is 123-45-6789" \
  --language-code en \
  --endpoint-url $AWS_ENDPOINT_URL

SDK Example (Java)

ComprehendClient comprehend = ComprehendClient.builder()
    .endpointOverride(URI.create("http://localhost:4566"))
    .region(Region.US_EAST_1)
    .credentialsProvider(StaticCredentialsProvider.create(
        AwsBasicCredentials.create("test", "test")))
    .build();

DetectSentimentResponse response = comprehend.detectSentiment(req -> req
    .text("Floci makes local AWS testing painless")
    .languageCode("en"));

System.out.println("Sentiment: " + response.sentiment());