Developer Tools
Twinning
Open-source tool that turns an OpenAPI spec or schema into a local, runnable twin
Twinning serves local twins of REST, Postgres, Snowflake, and MCP APIs and databases from OpenAPI specs and schemas, enabling safe testing without production
Overview
A look at cmdrvl.com
Twinning is an open-source Rust tool that creates runnable local twins of APIs and databases from OpenAPI documents and schemas. Point it at a specification and it serves a local twin with the same routes, authentication shape, and response schemas, with no backend required. The tool speaks REST, Postgres wire protocol, Snowflake wire protocol, and MCP, and can overlay measured live behavior on top of published specs to surface production quirks during testing.
Agents and test suites develop against the twin instead of production, eliminating risk to live systems and avoiding quota consumption. Teams building agents and data pipelines can use twins to safely test destructive calls, malformed requests, pagination edge cases, and other scenarios that need a safe environment for learning.
Feature notes
- REST API twin generation from OpenAPI spec
- Postgres wire protocol support
- Snowflake wire protocol support
- MCP server support
- Live behavior overlay on published specs
- One-command agent installation
- Deterministic test responses matching live behavior
Pricing
Pricing model: Open source
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FAQ
- What is Twinning for?
- Teams building agents and data pipelines use Twinning to have a safe place to test destructive calls, malformed requests, and edge cases without touching production. It provides a local twin that speaks the same protocols as the real API or database, letting agents and test suites develop against faithful behavior matching what they will encounter in production.
- How do you install Twinning with an agent?
- The fastest install is to provide your coding agent with the prompt from the README. The agent detects your operating system, downloads the latest release, verifies the checksum, runs a health check, and registers the MCP server with your client.
- How does Twinning differ from a hand-written mock?
- Twinning is not a hand-written mock. It speaks REST, the Postgres wire protocol, the Snowflake wire protocol, and MCP, and it can overlay measured live behavior on top of a published spec so production quirks show up in testing.
- What protocols does Twinning support?
- Twinning supports REST, Postgres wire protocol, Snowflake wire protocol, and MCP.
- How are CMD+RVL, Foodtruck AI LLC and Cairn related?
- CMD+RVL is the trading name of Foodtruck AI LLC. We operate Text Cairn and Hire Cairn. Text Cairn is our free research assistant over text. Hire Cairn is paid work with an agreed scope and price.
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