diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 69fffa0..f776d22 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -102,6 +102,44 @@ cargo test --workspace --features default -- --nocapture
 cargo test --workspace --features default test_name
 ```
 
+### SDK Conformance Tests
+
+pdftract includes a shared SDK conformance suite that validates the public API contract across all SDK implementations (Python, Node, Go, Java, .NET, and Rust). The Rust SDK conformance tests run directly against `pdftract-core` to ensure the library's public API satisfies the documented SDK contract.
+
+```bash
+# Run the conformance suite
+cargo test -p pdftract-core --test conformance
+
+# Run with specific features
+cargo test -p pdftract-core --test conformance --features ocr,profiles,remote,receipts
+```
+
+The conformance suite is defined in `tests/sdk-conformance/cases.json` and covers all 9 SDK contract methods:
+- `extract` — Full extraction with structured output
+- `extract_text` — Plain text extraction
+- `extract_markdown` — Markdown-formatted extraction
+- `extract_stream` — Streaming NDJSON extraction
+- `search` — Pattern search (literal and regex)
+- `get_metadata` — PDF metadata extraction
+- `hash` — Content fingerprinting (SHA256)
+- `classify` — Document classification
+- `verify_receipt` — Receipt verification
+
+Each test case includes:
+- **fixture** — Input PDF path or URL
+- **method** — Which SDK method to invoke
+- **options** — Method-specific options (OCR, password, etc.)
+- **expected** — Expected results with numeric tolerances
+- **tolerances** — Per-field numeric comparison tolerances
+- **feature** — Required feature flag (for conditional compilation)
+
+Feature-gated tests skip automatically when the corresponding feature is not compiled:
+- `ocr` — OCR-based extraction
+- `decrypt` — Password-protected PDFs
+- `profiles` — Document classification
+- `receipts` — Receipt verification
+- `remote` — URL-based remote fetch
+
 ## Minimum Supported Rust Version (MSRV)
 
 The **Minimum Supported Rust Version (MSRV)** for pdftract is **1.78**. This is the oldest Rust version that can successfully build the project. The MSRV is declared in `Cargo.toml` via the `rust-version` field and enforced in CI.
diff --git a/crates/pdftract-core/README.md b/crates/pdftract-core/README.md
index 196a2d3..699e8f4 100644
--- a/crates/pdftract-core/README.md
+++ b/crates/pdftract-core/README.md
@@ -26,6 +26,35 @@ The tradeoff—occasional merge conflicts when PRs update overlapping dependenci
 - `extract`: Text extraction with provenance (bounding boxes, confidence scores)
 - `ocr`: Tesseract integration for raster pages
 
+## Testing
+
+### SDK Conformance Tests
+
+The `conformance` integration test validates that `pdftract-core`'s public API satisfies the SDK contract shared across all language implementations. The test rig runs shared conformance cases from `tests/sdk-conformance/cases.json` and verifies correct behavior for all 9 SDK contract methods.
+
+```bash
+# Run the conformance suite
+cargo test --test conformance
+
+# Run with specific features
+cargo test --test conformance --features ocr,profiles,remote,receipts
+```
+
+The conformance suite covers:
+- `extract` — Full extraction with structured Document output
+- `extract_text` — Plain text extraction
+- `extract_markdown` — Markdown-formatted extraction with tables and headings
+- `extract_stream` — Streaming NDJSON extraction for large documents
+- `search` — Pattern search with regex and case-insensitive options
+- `get_metadata` — PDF metadata (page count, title, author, creator)
+- `hash` — Content fingerprinting (SHA256) with fast hash variant
+- `classify` — Document classification with category and confidence
+- `verify_receipt` — Receipt verification against signed metadata
+
+Each test case validates expected results with numeric tolerances for bounding boxes and confidence scores. Feature-gated tests (OCR, decryption, classification, receipts, remote) skip automatically when the corresponding feature is not compiled.
+
+See `CONTRIBUTING.md` for more details on the conformance suite and adding new test cases.
+
 ## Usage
 
 ```rust