Borrowing it
Nothing to install: this file belongs to managedcode/PrompterOne. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/managedcode/PrompterOne/main/.codex/skills/dotnet-modern-csharp/SKILL.mdgit clone --depth 1 https://github.com/managedcode/PrompterOneWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/managedcode/prompterone/dotnet-modern-csharp)<a href="https://agentmods.dev/skills/managedcode/prompterone/dotnet-modern-csharp"><img src="https://agentmods.dev/badge/skills/managedcode/prompterone/dotnet-modern-csharp/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/managedcode/prompterone/dotnet-modern-csharp"><img src="https://agentmods.dev/badge/skills/managedcode/prompterone/dotnet-modern-csharp.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00053 | $0.01186 |
| Opus 5.5 | $0.00021 | $0.00474 |
| Sonnet 5.5 | $0.00011 | $0.00237 |
| Haiku 4.5 | $0.00005 | $0.00119 |
Grade A, and why
dotnet-modern-csharp scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
Copies of this mod
4 near-identical copies found in the catalogue:
- modern-csharp — 97% identical, 6 lines differ
- dotnet-modern-csharp — 97% identical, 2 lines differ
- mcaf-dotnet-features — 95% identical, 16 lines differ
- mcaf-dotnet-features — 95% identical, 16 lines differ
How it starts
The opening of the file, as written. The whole thing — 120 lines — stays where its author put it; the contents beside it link to each section on GitHub.
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
TFMorTFMs - explicit
LangVersion, if any - current SDK version
- team style rules in
.editorconfigandAGENTS.md
Quick Start
- Read the nearest
AGENTS.mdand confirm scope and constraints. - Run this skill's
Workflowthrough theRalph Loopuntil outcomes are acceptable. - Return the
Required Result Formatwith 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.
- Pay special attention to C# 13 and C# 14:
- C# 13 is the stable language for
.NET 9 - C# 14 is the stable language for
.NET 10
- C# 13 is the stable language for
- When feature selection changes architecture, style rules, or generated-code patterns, coordinate with:
dotnetdotnet-analyzer-configdotnet-architecture
- After feature-driven refactors, run the repo's .NET quality pass through
dotnet.
Bootstrap When Missing
If the requested C# feature depends on SDK or language support the repo does not have yet:
What ships with it
4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 120 lines · 53 tokens per session scan A 981b52bb59a5
dotnet-modern-csharp is a skill published in the GitHub repository managedcode/PrompterOne (45 stars, last pushed 5mo ago), licensed MIT. It adds 53 tokens to every session and 1,186 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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