Orca MCP Server

Orca

Orchestrated State Machine Language — a two-layer architecture for reliable LLM code generation.

The core insight: LLMs generate flat transition tables reliably, but they struggle to guarantee topology correctness on their own. Orca separates program structure (state machine topology) from computation (action functions), then verifies the structure automatically before any code runs.

Machines are written in plain Markdown — a format LLMs can read and write natively.

What it looks like

# machine PaymentProcessor

## context

| Field       | Type    | Default |
|-------------|---------|---------|
| order_id    | string  |         |
| amount      | decimal |         |
| retry_count | int     | 0       |

## events

- submit_payment
- payment_authorized
- payment_declined
- retry_requested
- settlement_confirmed

## state idle [initial]
> Waiting for a payment submission

## state authorizing
> Waiting for payment gateway response
- on_entry: send_authorization_request

## state declined
> Payment was declined

## state settled [final]
> Payment fully settled

## transitions

| Source      | Event                | Guard      | Target      | Action           |
|-------------|----------------------|------------|-------------|------------------|
| idle        | submit_payment       |            | authorizing |                  |
| authorizing | payment_authorized   |            | settled     |                  |
| authorizing | payment_declined     |            | declined    |                  |
| declined    | retry_requested      | can_retry  | authorizing | increment_retry  |
| declined    | retry_requested      | !can_retry | settled     | record_failure   |

## gu

The verifier checks this before anything runs: reachability, deadlocks, guard determinism, orphan declarations, and effect consistency.

Features

Language

• States with [initial] / [final] markers, descriptions, onentry / onexit actions
• Transitions as a flat table — the format LLMs generate most reliably
• Guard expressions: comparisons, boolean logic, null checks
• Hierarchical (nested) states
• Parallel regions with all-final / any-final / custom sync strategies
• Timeouts: timeout: 30s -> state_name
• Ignored events: ignore: EVENT_NAME
• Machine invocation: one machine calling another, with input mapping and completion events
• Multi-machine files: multiple machines in one .orca.md separated by ---
• ## effects section: named I/O schemas for external side effects
• Decision tables: co-located conditional logic without guard explosion — verified for completeness, consistency, and cross-machine reachability

Shortened. The full README is on GitHub.