snippet-eval

Snippet and Script Evaluation

You use analyze_snippet and evaluate_csharp for fast feedback when loading a full .sln is unnecessary or impossible.

Input

$ARGUMENTS should indicate either:

• A short C# fragment to analyze or run, or
• A file path to read and treat as snippet/script (if the user points at a scratch file)

Server discovery

Full solution workflows live in roslyn://server/catalog. This skill is for ephemeral analysis only.

When to use which tool

Goal	Tool
Parse, bind, diagnostics on a fragment	analyze_snippet
Run a script / evaluate an expression (side effects, output)	evaluate_csharp
Production refactor / cross-file impact	Load workspace with workspace_load and use symbol tools

Workflow

1. For compile/bind questions: call analyze_snippet with the code and appropriate options (as exposed by the tool schema).
2. For execution: call evaluate_csharp; warn the user that scripts run in the host process trust boundary.
3. If results imply real-project dependencies, recommend workspace_load on the actual solution.

Explain mode — semantic walk-through for teaching or learning

Invoke with --explain or ask "explain this snippet" / "what does this do?". The skill produces a step-by-step semantic walkthrough instead of a pass/fail result:

1. Call analyze_snippet to bind the snippet and gather diagnostics.
2. Call get_operations (if available) on the snippet to walk the IOperation tree — this yields the full semantic tree: local declarations, invocations, branches, loops, lambdas, await points.
3. For each top-level construct (declaration, expression, statement):
   • Name the operation kind (e.g., LocalReference, InvocationOperation, ConditionalAccessOperation)
   • State the inferred type and (for numeric/string literals) the value
   • Explain data-flow implications: what variables are read, what gets assigned, what captures (for lambdas/closures)
4. If the snippet uses await, show the async flow: where the state machine suspends, what continuation happens on completion vs exception.
5. If the snippet uses LINQ, explain deferred vs immediate execution and what the query translates to.
6. Conclude with a single-sentence summary: "This snippet X, producing Y, with no/these side effects."

Explain mode is read-only — it never calls evaluate_csharp. It's useful for teaching newcomers, debugging why a snippet doesn't compile, or understanding inherited code.

Safety

Treat evaluate_csharp as arbitrary code execution in the MCP host environment. Only run code the user explicitly supplied and avoid secrets in snippets. Explain mode is safe — it never executes.