Write modern, version-aware C# for .NET repositories while staying compatible with the repo's target framework and language-version policy. USE FOR: modern idiomatic C# code; language-version compatibility decisions; upgrading or reviewing C# feature usage across versions. DO NOT USE FOR: non-C# .NET languages such as F# or VB; analyzer-only or formatter-only setup with no language feature choice. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, o
SkillScore77Maintained
Automatic
◆Coding pack
Last verified 8/19/2026
What it changes
Passed 13 of 17 test cases with the skill, and 10 of 17 without it.
Without skill59%
With skill77%
Checks it passed that the model alone missed
Declines the request as outside C# language scope.
Instructs checking local SDKs using dotnet --list-sdks.
Declines Visual Basic .NET refactoring as outside C# language scope.
and 1 more in the full report
4 fixed13 passed either way5 still failing0 broke
Pass-rate lift
+18 pp
Tokens
+37%
Agent turns
0%
Response time
-35%
Model gemini-3.6-flashMeasured 8/19/2026v217 of 22 cases passed with skill · 17 comparable
Tokens, turns and time describe resource use, not a dollar price.
See it in action
One of 4 test cases the skill fixed. Same model, same prompt, with and without the skill.
1 of 4
Prompt
Our project targets `.NET Framework 4.8` and the team has explicitly decided to stay on C# 7.3 and not upgrade toolchains or language versions. A developer requested using C# 13 field keywords in this project. What status should be reported when evaluating this request?
What was checked, without and with the skill
Checked
Without skill
With skill
Returns status as not_applicable when intentionally staying below required language level.
Missed
Passed
Notes that the repository explicitly remains on an older language version.
Passed
Passed
case-13 · gemini-3.6-flash · 8/19/2026 · answers are capped and redacted
What's inside
The instructions your model reads when the skill loads.
SKILL.md118 lines4 files
Modern C# for .NET
Trigger On
the repo wants more modern idiomatic C# code
a change depends on language-version compatibility
the team is upgrading or reviewing C# feature usage across versions
you need to know whether a C# 13 or C# 14 feature is safe to use
Value
produce a concrete project delta: code, docs, config, tests, CI, or review artifact
reduce ambiguity through explicit planning, verification, and final validation skills
leave reusable project context so future tasks are faster and safer
Do Not Use For
non-C# .NET languages such as F# or VB
analyzer-only or formatter-only setup with no language feature choice
Inputs
target TFM or TFMs
explicit LangVersion, if any
current SDK version
team style rules in .editorconfig and AGENTS.md
Quick Start
Read the nearest AGENTS.md and confirm scope and constraints.
Run this skill's Workflow through the Ralph Loop until outcomes are acceptable.
Return the Required Result Format with concrete artifacts and verification evidence.
Workflow
Detect the real language ceiling from the repo's target framework and explicit LangVersion.
Prefer stable features that the current repo actually supports.
Use modern syntax when it reduces ceremony, improves correctness, or makes invariants clearer.
Do not mass-rewrite a codebase into newer syntax unless the repo wants that churn.
Treat preview features as opt-in only. Never assume preview because the current machine has a newer SDK.