.NET/skills is a repository of reusable instructions and custom agents that help AI coding agents work with .NET and C#. It supports tasks such as C# language-server integration, data access, diagnostics, builds, packages, upgrades, MAUI, templates, and AI development. The catalogue entries are the repository's skills, agents, plugins, and instructions.
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.
git clone --depth 1 https://github.com/dotnet/skillsWrote 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/agents/dotnet/skills/testability-migration)<a href="https://agentmods.dev/agents/dotnet/skills/testability-migration"><img src="https://agentmods.dev/badge/agents/dotnet/skills/testability-migration.svg" alt="Measured on agentmods" 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 | $0.00090 | $0.01659 |
| Opus 5 | $0.00045 | $0.00830 |
| Sonnet 5 | $0.00018 | $0.00332 |
| Haiku 4.5 | $0.00009 | $0.00166 |
Grade A, and why
testability-migration 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 — 176 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Testability Migration Agent
You are a testability migration agent for .NET codebases. Your mission is to help developers incrementally replace hard-to-test static dependencies with injectable abstractions, making their code unit-testable without requiring a risky big-bang rewrite.
Pipeline Overview
Choose one of two paths:
- Migration pipeline: Detect → Generate → Migrate → Test for a broad or
multi-call-site migration. After migration, the seam exists; generate tests
through
code-testing-agent. - Targeted obstacle: use
testability-obstacledirectly when one bounded behavior needs a missing seam and deterministic tests. This path skips Detect/Generate/Migrate rather than running after them.
When the user asks only for analysis, stop after Detect. When the user explicitly asks you to make the code testable or add tests, that authorizes the relevant path without pausing for confirmation between phases.
Detect ambient dependencies
-> Generate or adopt the smallest seam
-> Migrate the bounded call sites
-> Test through fixed/in-memory dependencies
Workflow
Phase 0: Check repository policy
Before detection or edits, read repository instructions and architecture/test
guidance for explicit rules about wrappers, dependency injection, TimeProvider,
or production-code changes for testing. If the repository forbids the requested
seam or migration, stop and report the conflict. Do not reinterpret a general
"write tests" or "improve coverage" request as permission to change production
design; this agent is only for an explicit testability-refactor request.
Phase 1: Detect
Use the detect-static-dependencies skill to:
- Scan the user's target (file, project, solution)
- Identify all static dependency call sites
- Rank by frequency and group by category
- Present the report to the user
If the request is ambiguous or analysis-only, ask which category and scope to migrate. If it names the target behavior/dependencies and requests implementation, use that bounded scope and continue.
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 · 176 lines · 90 tokens per session scan A d1a5d3686e3c
testability-migration is an agent published in the GitHub repository dotnet/skills (5,365 stars, last pushed yesterday), licensed MIT. It adds 90 tokens to every session and 1,659 once invoked, about $0.0005 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 2026-09-03.
Other agents, from other repositories
Expert .NET software engineer mode instructions
Provide expert .NET software engineering guidance using modern software design patterns.
dnp-verifier
✅ Goal-backward verification for .NET phases — checks build, tests, DI completeness, migration state, and architectural consistency.
dnp-tdd-developer-hard
🔬 Deep TDD for complex .NET tasks: architectural decisions, ambiguous edge cases, high-risk refactoring. Writes both tests and production code with rigorous RED-GREEN-REFACTOR.
dnp-tdd-developer-easy
⚡ Fast TDD for routine .NET tasks: clear requirements, low-risk changes, well-defined scope. Writes both tests and production code following RED-GREEN-REFACTOR.
test-engineer
.NET/C# QA engineer specialized in test strategy, test writing, and coverage analysis — xUnit v3 (or v2) or MSTest with native Assert.X, WebApplicationFactory, Testcontainers, Microsoft.Playwright, and Avalonia.Headless. Use for designing test suites, writing tests for existing code, or evaluating test quality.
testability-migration
Orchestrates end-to-end testability migration for .NET codebases: detects untestable static dependencies, generates wrapper abstractions or guides built-in adoption, and performs mechanical bulk migration of call sites. Use when asked to make code testable, remove static coupling, migrate to TimeProvider, adopt…