AI skill for Yulin

The yulin-aws-simulation skill gives coding agents instructions for using Yulin in tests and local development.

Install the skill

Install it in the current project’s .agents/skills/ directory:

npx @kensio/skills add yulin-aws-simulation

Codex CLI, Cursor, VS Code, and Gemini CLI read skills from that directory. To install the skill for Claude Code, add --agent claude. Add --user to install it for every project under your user account.

Claude Code can also install the skill from the Kensio plugin marketplace:

claude plugin marketplace add KensioSoftware/kensio.ai
claude plugin install yulin-aws-simulation@kensio

The skill is also published as the @kensio/yulin-aws-simulation npm package. Each kensio.ai release includes a zip archive for installations that cannot reach a package registry.

What the skill teaches

The skill tells an agent how to:

• use SimAws and SimSdk directly
• deploy the same synthesized CDK template in tests and local development
• choose between deploying a resource and registering one directly
• intercept AWS SDK clients without keeping separate hand-written stubs
• control simulated time
• inspect simulated state in assertions
• match simulated service errors by name
• share one simulated deployment and SDK interception across a whole test suite
• give tests that control simulated time their own isolated Yulin environment
• invoke code through a simulated Lambda function with its configured role and environment
• treat unsupported behaviour as a gap to report, not behaviour to guess

The test suite setup guide states the default explicitly. An agent should set Yulin up once for the suite and let tests share it as they would share an AWS account or a container-based simulator. Tests that move the shared simulated clock are the main exception.

Give the agent access to the API docs

The skill covers testing choices. The service guides document Yulin’s APIs and supported AWS behaviour.

The skill points agents to yulinsim.dev/llms.txt. That file indexes plain Markdown versions of every guide on the documentation site. Append llms.txt to a page URL to read that page as Markdown.

The npm package includes the same documentation under node_modules/@kensio/yulin/docs/. Its index is node_modules/@kensio/yulin/llms.txt. These files match the installed Yulin version and remain available without network access. Some search tools skip node_modules unless the path is given explicitly.

Limitations

• The skill does not replace the service guides. An agent still needs the relevant guide when it works with a service command, event shape, or limitation.
• The skill is versioned separately from Yulin. The documentation included in the installed Yulin package is the reference for that package version.

The skill source is available at kensio.ai/skills/yulin-aws-simulation under the Apache-2.0 licence.