Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/codewithmukesh/dotnet-claude-kit/modern-csharpnpx skills add codewithmukesh/dotnet-claude-kit --skill modern-csharpgit clone --depth 1 https://github.com/codewithmukesh/dotnet-claude-kitWhat 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 | $0.00110 | $0.01620 |
| Opus 5 | $0.00055 | $0.00810 |
| Sonnet 5 | $0.00022 | $0.00324 |
| Haiku 4.5 | $0.00011 | $0.00162 |
Grade A, and why
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 3d 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.
How it starts
The opening of the file, as written. The whole thing — 197 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Modern C# (C# 14 / .NET 10)
Core Principles
- Use the newest stable features — C# 14 is the target. Prefer language-level constructs over library workarounds.
- Readability over cleverness — Pattern matching and expression-bodied members improve readability when used appropriately; deeply nested patterns do not.
- Value types where possible — Prefer
record struct,Span<T>, and stack allocation to reduce GC pressure. - Immutability by default — Use
record,readonly,init, andrequiredto make illegal states unrepresentable.
Patterns
Well-Known Features Quick Reference
| Feature | Usage | Example |
|---|---|---|
| Primary constructors | DI injection, eliminate field assignments | public class OrderService(IOrderRepo repo, TimeProvider clock) { } |
| Collection expressions | [] for all collection types + spread |
List<string> names = ["Alice", "Bob"]; / int[] all = [..a, ..b, 99]; |
| Records | DTOs, value objects, immutable data | public record CreateOrderRequest(string CustomerId, List<OrderItem> Items); |
readonly record struct |
Small stack-allocated value types | public readonly record struct Money(decimal Amount, string Currency); |
| Pattern matching | Switch expressions, list/property patterns | order switch { { Total: > 1000 } => "Premium", _ => "Standard" }; |
| List patterns | Deconstruct arrays/lists | items switch { [] => "Empty", [var x] => $"One: {x}", [var f, .., var l] => $"{f}..{l}" }; |
Span<T> |
Zero-allocation slicing | ReadOnlySpan<char> trimmed = input.Trim(); int.TryParse(trimmed[4..], out id); |
| Raw string literals | Multi-line SQL, JSON, XML | var sql = """ SELECT ... """; / interpolated: $$""" {"id": "{{id}}"} """; |
required members |
Enforce initialization | public required string ConnectionString { get; init; } |
is pattern + extraction |
Null/type/property check | if (result is { IsSuccess: true, Value: var order }) { ... } |
The field Keyword (C# 14)
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.
- 3d ago First seen · 197 lines · 110 tokens per session scan A bc23e927c4a7
modern-csharp is a skill published in the GitHub repository codewithmukesh/dotnet-claude-kit (689 stars, last pushed 26d ago), licensed MIT. It adds 110 tokens to every session and 1,620 once invoked, about $0.0006 per session on Opus 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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