SDKs - Local Web Services

Available

Python

pytest integration, DynamoDB / SQS / S3 helpers, fluent faking and chaos APIs

Available

TypeScript

Jest / Vitest integration, AWS SDK v3 clients, faking and chaos APIs

Available

JavaScript

Jest / Mocha integration, AWS SDK v3 clients, automatic endpoint redirection via env vars

Available

Java

JUnit 5 integration for Java and Kotlin projects, AWS SDK v2 clients, try-with-resources lifecycle

Available

Go

Go testing package integration, AWS SDK v2 clients, auto-discovery from HCL

Why use an SDK?

ldk dev (local server)

Runs as an external process
Services start on network ports (3000–3030)
Works with any language or framework
Supports hot reloading for Lambda handlers
Web dashboard at /_ldk/gui
Reads CDK or HCL projects

Language SDK (in-process)

Runs as threads in your test process
No ports, no networking overhead
Native test framework integration (pytest, Jest…)
Per-test state isolation with session.reset()
Fluent APIs for faking and chaos injection
Auto-discovers resources from CDK or HCL

Python SDK Highlights

The Python SDK (local-web-services-python-sdk) provides everything you need to test AWS-backed Python applications without leaving your pytest suite.

🔄

LwsSession

A single context manager that starts all your services. Declare tables, queues, buckets, topics, state machines, parameters, and secrets — or auto-discover them from a CDK or HCL project.

👥

pytest Fixtures

Zero-boilerplate pytest integration. The lws_session fixture starts services once per session; lws_reset wipes state between tests automatically.

📋

Resource Helpers

Simplified DynamoDB, SQS, and S3 helpers with built-in assertion methods: table.assert_item_exists(), queue.assert_message_count(), bucket.assert_object_count().

🎭

Operation Faking

Override any AWS operation response with a fluent builder. Inject throttling errors, custom status codes, or delayed responses at the operation level without changing application code.

💥

Chaos Engineering

Inject error rates, latency ranges, connection resets, and timeouts into any service. Apply and clear chaos scenarios programmatically within individual test functions.

🔒

IAM Authorization

Switch IAM modes to disabled, audit, or enforce. Define named identities with inline allow/deny policies and verify authorization behavior in tests.

Python SDK Docs GitHub

Quick Start: Python

Install the SDK and write your first test in minutes.

Install

              pip install local-web-services-python-sdk
# or with uv
uv add local-web-services-python-sdk
            

Declare your resources

              from lws_testing import LwsSession

with LwsSession(
    tables=[{"name": "Orders", "partition_key": "id"}],
    queues=["OrderQueue"],
    buckets=["ReceiptsBucket"],
) as session:
    # services are running
    pass
            

Write a test

              def test_create_order(lws_session):
    # Use a boto3 client pointing to local services
    client = lws_session.client("dynamodb")
    client.put_item(
        TableName="Orders",
        Item={"id": {"S": "42"}, "status": {"S": "pending"}}
    )

    # Or use the DynamoDB helper with assertions
    table = lws_session.dynamodb("Orders")
    table.assert_item_exists({"id": {"S": "42"}})
            

Configure pytest fixtures

              # conftest.py
import pytest
from lws_testing import LwsSession

@pytest.fixture(scope="session")
def lws_session_spec():
    return {
        "tables": [{"name": "Orders", "partition_key": "id"}],
        "queues": ["OrderQueue"],
        "buckets": ["ReceiptsBucket"],
    }

# lws_session and lws_reset fixtures are provided
# automatically by the lws_testing pytest plugin
            

Full Python SDK Reference