🐙 Mocktopus

Multi-armed mocks for LLM apps

Mocktopus is a drop-in replacement for OpenAI/Anthropic APIs, designed to make your LLM application tests fast, deterministic, and cost-free.

Why Mocktopus?

Testing LLM applications is challenging:

• Non-deterministic: Same prompt, different responses
• Expensive: Every test run costs API credits
• Slow: API calls add latency to test suites
• Network-dependent: Can't run tests offline
• Complex workflows: Tool calls and streaming complicate testing

Mocktopus solves these problems by providing a local mock server that perfectly mimics LLM APIs.

Features

✅ Drop-in replacement - Just change your base URL ✅ Deterministic responses - Same input → same output ✅ Tool/function calling - Full support for complex workflows ✅ Streaming - Server-sent events (SSE) support ✅ Multiple providers - OpenAI and Anthropic compatible ✅ Zero cost - No API charges for tests ✅ Fast - No network latency ✅ Offline - Run tests without internet

Installation

pip install mocktopus

Quick Start

1. Create a scenario file (scenario.yaml):

version: 1
rules:
  - type: llm.openai
    when:
      model: "gpt-4*"
      messages_contains: "hello"
    respond:
      content: "Hello! How can I help you today?"

2. Start the mock server:

mocktopus serve -s scenario.yaml

3. Point your app to Mocktopus:

from openai import OpenAI

# Instead of the real API:
# client = OpenAI(api_key="sk-...")

# Use Mocktopus:
client = OpenAI(
    base_url="http://localhost:8080/v1",
    api_key="mock-key"  # Any string works
)

response = client.chat.completions.create(
    model="gpt-4",
    messages=[{"role": "user", "content": "hello"}]
)
print(response.choices[0].message.content)
# Output: "Hello! How can I help you today?"

Usage Modes

Mock Mode (Default)

Use predefined YAML scenarios for deterministic responses:

mocktopus serve -s examples/chat-basic.yaml

Record Mode (Coming Soon)

Proxy and record real API calls for later replay:

mocktopus serve --mode record --recordings-dir ./recordings

Replay Mode (Coming Soon)

Replay previously recorded API interactions:

mocktopus serve --mode replay --recordings-dir ./recordings

Scenario Examples

Basic Chat Response

version: 1
rules:
  - type: llm.openai
    when:
      messages_contains: "weather"
    respond:
      content: "It's sunny today!"

Function Calling

version: 1
rules:
  - type: llm.openai
    when:
      messages_contains: "weather"
    respond:
      tool_calls:
        - id: "call_123"
          type: "function"
          function:
            name: "get_weather"
            arguments: '{"location": "San Francisco"}'

Streaming Response

version: 1
rules:
  - type: llm.openai
    when:
      model: "*"
    respond:
      content: "This will be streamed..."
      delay_ms: 50  # Delay between chunks
      chunk_size: 5  # Characters per chunk

Limited Usage

version: 1
rules:
  - type: llm.openai
    when:
      messages_contains: "test"
    times: 3  # Only responds 3 times
    respond:
      content: "Limited response"

CLI Commands

Start Server

# Basic usage
mocktopus serve -s scenario.yaml

# Custom port
mocktopus serve -s scenario.yaml -p 9000

# Verbose logging
mocktopus serve -s scenario.yaml -v

Test Scenarios

# Validate a scenario file
mocktopus validate scenario.yaml

# Simulate a request without starting server
mocktopus simulate -s scenario.yaml --prompt "Hello"

# Generate example scenarios
mocktopus example --type basic > my-scenario.yaml
mocktopus example --type tools > tools-scenario.yaml

Testing with Mocktopus

Pytest Integration

import pytest
from mocktopus import use_mocktopus

def test_my_llm_app(use_mocktopus):
    # Load scenario
    use_mocktopus.load_yaml("tests/scenarios/test.yaml")

    # Get a client
    client = use_mocktopus.openai_client()

    # Test your app
    response = client.chat.completions.create(
        model="gpt-4",
        messages=[{"role": "user", "content": "test"}]
    )
    assert "expected" in response.choices[0].message.content

Continuous Integration

# .github/workflows/test.yml
name: Tests
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
      - run: pip install -e .
      - run: mocktopus serve -s tests/scenarios.yaml &
      - run: pytest  # Your tests hit localhost:8080

Advanced Features

Pattern Matching

Mocktopus supports multiple matching strategies:

• Exact match: messages_contains: "exact phrase"
• Regex: messages_regex: "\\d+ items?"
• Glob: model: "gpt-4*"

Response Configuration

respond:
  content: "Response text"
  delay_ms: 100  # Simulate latency
  usage:
    input_tokens: 10
    output_tokens: 20
  # For streaming
  chunk_size: 10  # Characters per chunk

Roadmap

• OpenAI chat completions API
• Streaming support (SSE)
• Function/tool calling
• Anthropic messages API
• Recording & replay
• Embeddings API
• Assistants API
• Image generation
• Semantic similarity matching
• Response templating
• Load testing mode

Contributing

We welcome contributions! See our Contributing Guide for details.

License

MIT - See LICENSE for details.

Links

• GitHub Repository
• PyPI Package
• Documentation
• Issue Tracker

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