Explicator

Provider-agnostic natural language AI interface for scenario-driven analytical modelling

Explicator bridges the gap between complex analytical models and the people who need to understand them. Ask a question in plain English, it identifies the right scenarios to run, executes them against your model, and returns a clear explanation of what the results mean. No model expertise required.

Provider-agnostic by design, Explicator works with Claude, Azure OpenAI, Copilot, or any LLM your organisation uses.

---

Architecture

Explicator follows a ports & adapters (hexagonal) architecture. The domain and application layers contain no framework code — adapters translate between external interfaces and the core ModelService.

graph TB
    subgraph Entry Points
        CLI["CLI\n(Click)"]
        MCP["MCP Server\n(FastMCP)"]
        Chat["Chat REPL"]
    end

    subgraph AI Layer
        Providers["AI Providers\nClaude · Azure OpenAI"]
        Dispatcher["Tool Dispatcher"]
        ToolDefs["Tool Definitions\n(OpenAI JSON Schema)"]
    end

    subgraph Application Layer
        Service["ModelService\nBusiness Logic"]
    end

    subgraph Domain Layer
        Models["Domain Models\nInputField · OutputField\nModelSchema · ScenarioDefinition\nScenarioResult · Override\nScenarioComparison"]
        Ports["Abstract Ports\nScenarioRunner\nModelRepository"]
    end

    subgraph Infrastructure
        InMem["In-Memory Adapters\nInMemoryModelRepository\nFunctionalScenarioRunner"]
        YourModel["Your Model\n(any Python callable)"]
    end

    CLI --> Service
    MCP --> Service
    Chat --> Dispatcher
    Chat --> Providers
    Providers --> ToolDefs
    Dispatcher --> Service
    Service --> Ports
    Ports -.->|implemented by| InMem
    InMem --> YourModel

    style Service fill:#4a9eda,color:#fff
    style Models fill:#6bc96b,color:#fff
    style Ports fill:#6bc96b,color:#fff
    style CLI fill:#f5a623,color:#fff
    style MCP fill:#f5a623,color:#fff
    style Chat fill:#f5a623,color:#fff

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---

Project Structure

explicator/
├── src/explicator/
│   ├── domain/              # Core data structures and abstract ports
│   │   ├── models.py        # ScenarioDefinition, ScenarioResult, ModelSchema, etc.
│   │   └── ports.py         # ScenarioRunner, ModelRepository (abstract interfaces)
│   ├── application/
│   │   └── service.py       # ModelService — single entry point for all business logic
│   ├── adapters/
│   │   ├── cli/             # Click-based CLI adapter
│   │   ├── mcp_server/      # FastMCP server adapter (for Claude Desktop / MCP clients)
│   │   └── data/            # Infrastructure adapters (in-memory implementations)
│   ├── ai/
│   │   ├── tools/           # Tool definitions in OpenAI function-calling JSON schema format
│   │   ├── providers/       # Provider adapters: Claude, Azure OpenAI (+ abstract base)
│   │   └── dispatcher.py    # Shared tool dispatcher (provider-agnostic)
│   └── config.py            # Configuration via environment variables
├── examples/
│   └── demo_model/          # Bond portfolio risk model — shows how to wire Explicator
├── docs/
│   └── model_schema.md      # Rich domain description for AI context
└── tests/
    ├── unit/
    └── integration/

explicator is the library — install it as a dependency and build your model on top of it, just as you would with fastapi or click. Your model code lives in your own project; explicator provides the service layer, AI interface, CLI, and MCP server.

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Quick Start

1. Install

uv sync --extra claude --extra dev

For Azure OpenAI instead:

uv sync --extra azure --extra dev

Or with pip:

pip install -e ".[claude,dev]"

2. Configure

cp .env.example .env
# Edit .env and set your API key and provider

3. Run the demo CLI

# List scenarios
explicator --service examples.demo_model.model:build_service scenarios

# Run a scenario
explicator --service examples.demo_model.model:build_service run base_case

# Run with an override
explicator --service examples.demo_model.model:build_service run base_case -o credit_spread_ig=2.5

# Compare two scenarios
explicator --service examples.demo_model.model:build_service compare base_case credit_stress

# Chat with an AI about the model
explicator --service examples.demo_model.model:build_service chat

Set EXPLICATOR_SERVICE in your environment to avoid repeating the flag:

export EXPLICATOR_SERVICE=examples.demo_model.model:build_service
explicator run base_case
explicator chat "what happens to duration in the stagflation scenario?"

4. Start the MCP Server

With the demo model:

uv run mcp dev examples/demo_model/run_mcp.py

Via the entry point:

explicator-mcp examples.demo_model.model:build_service
# or
python -m explicator.adapters.mcp_server examples.demo_model.model:build_service

5. Connect Claude Desktop

Copy claude_desktop_config.json.example into your Claude Desktop config:

{
  "mcpServers": {
    "explicator": {
      "command": "uv",
      "args": [
        "run",
        "python",
        "-m",
        "explicator.adapters.mcp_server",
        "myapp.model:build_service"
      ],
      "env": {
        "ANTHROPIC_API_KEY": "your-api-key-here"
      }
    }
  }
}

Then ask Claude things like:

• "Run the credit stress scenario and tell me what happened to portfolio duration."
• "Override the credit spread input to 250bps and rerun the base case."
• "What are the key assumptions in this model?"
• "Compare the stagflation and rates_shock_up scenarios."

---

Connecting Your Own Model

explicator is a library — your model code lives in your own project. A typical layout:

my-risk-app/
├── pyproject.toml           # dependencies = ["explicator[claude]"]
├── .env                     # ANTHROPIC_API_KEY=...
└── src/myapp/
    ├── model.py             # schema, scenarios, model_fn, build_service()
    └── run_mcp.py           # calls explicator.run_mcp(service)

# src/myapp/model.py
import explicator

service = explicator.create(
    model_fn=my_model_fn,
    base_inputs=MY_BASE_INPUTS,
    schema=MY_SCHEMA,
    scenarios=MY_SCENARIOS,
)

# src/myapp/run_mcp.py
import explicator
from myapp.model import service

if __name__ == "__main__":
    explicator.run_mcp(service)

# CLI — point --service at any module:attribute that returns a ModelService
explicator --service myapp.model:service scenarios
explicator --service myapp.model:service run base_case
explicator --service myapp.model:service chat

Explicator uses the ports & adapters pattern. The quickest way to wire up any Python model function:

import explicator

def my_model(inputs: dict) -> dict:
    # Your model logic here
    return {"metric_a": ..., "metric_b": ...}

service = explicator.create(
    model_fn=my_model,
    base_inputs=MY_BASE_INPUTS,
    schema=MY_SCHEMA,
    scenarios=MY_SCENARIOS,
)

if __name__ == "__main__":
    explicator.run_mcp(service)

For custom storage or execution backends, implement ScenarioRunner and ModelRepository directly and pass them to ModelService:

from explicator import ModelService
from explicator.domain.ports import ScenarioRunner, ModelRepository

class MyRunner(ScenarioRunner): ...
class MyRepository(ModelRepository): ...

service = ModelService(runner=MyRunner(), repository=MyRepository())

See examples/demo_model/model.py for a complete worked example.

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AI Provider Configuration

Set AI_PROVIDER in your environment:

Value	Provider	Required env vars
claude (default)	Anthropic Claude	ANTHROPIC_API_KEY
azure_openai	Azure OpenAI	AZURE_OPENAI_API_KEY, AZURE_OPENAI_ENDPOINT, AZURE_OPENAI_DEPLOYMENT

Tool definitions live in src/explicator/ai/tools/definitions.py in OpenAI function-calling JSON schema format — a single source of truth consumed by all providers.

---

Running Tests

uv run pytest

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Layer Responsibilities

Layer	Location	Role
Domain	domain/	Pure Python dataclasses and abstract interfaces — no framework code
Application	application/service.py	Business logic via ModelService — no framework code, tested directly
Adapters	adapters/	Thin translation layers — CLI and MCP server both call ModelService
AI	ai/	Provider adapters, tool definitions, and dispatcher — no business logic

The MCP server and CLI are parallel entry points into the same application layer. They share no code with each other except through ModelService.