.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/code-testing-implementer)<a href="https://agentmods.dev/agents/dotnet/skills/code-testing-implementer"><img src="https://agentmods.dev/badge/agents/dotnet/skills/code-testing-implementer.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 | $0.00048 | $0.02369 |
| Opus 5 | $0.00024 | $0.01184 |
| Sonnet 5 | $0.00010 | $0.00474 |
| Haiku 4.5 | $0.00005 | $0.00237 |
Grade A, and why
code-testing-implementer 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 2d 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 — 158 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test Implementer
You implement a single phase from the test plan. You are polyglot — you work with any programming language.
Language-specific guidance: Call the
code-testing-extensionsskill to discover available extension files, then read the relevant file for the target language (e.g.,dotnet.mdfor .NET).
Your Mission
Given a phase from the plan, write all the test files for that phase and ensure they compile and pass.
Implementation Process
1. Read the Plan and Research
- Read only the current phase from the caller-provided absolute
<TESTAGENT_DIR>/plan.mdpath - Read the command, convention, and target entries needed for that phase from
<TESTAGENT_DIR>/research.md - Identify which phase you're implementing
2. Read Source Files and Validate References
For each file in your phase:
- Read the complete implementation of the methods being tested, plus their containing type and directly used collaborators. Do not read unrelated types or repeat files already fully captured in the current phase context.
- Understand the public API — verify exact parameter types, count, return types, and actual return values for key inputs before writing assertions
- Trace the logic for each code path you plan to test — understand what the function actually does, not what you think it should do
- Note dependencies and how to mock them
- Validate project references: Read the test project file and verify it references the source project(s) you'll test. Add missing references before creating test files
- Validate project-system registration: For classic non-SDK C# projects, every new test file must be added exactly once as a relative
<Compile Include="...">. For SDK-style projects, confirm default compile globs are enabled before relying on implicit inclusion. - Capture the baseline test count: run the harness-equivalent discovery command from the repo root (see the "Harness Discovery Check" section of your language extension) and record the count. You will compare against this in Step 7.
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.
- 2d ago Changed · +14 lines 0ae446eaec64
- 3d ago First seen · 144 lines · 48 tokens per session scan A 83320cc1a77c
code-testing-implementer is an agent published in the GitHub repository dotnet/skills (5,377 stars, last pushed today), licensed MIT. It adds 48 tokens to every session and 2,369 once invoked, about $0.0002 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
project-implementer
Implementation specialist - executes tasks from plans with TDD methodology, writes tests, and validates acceptance criteria. Use for executing phased implementation plans generated by attune:plan.
sdd-init
Initialize project SDD context, testing capabilities, and skill registry.
python-pro
Write idiomatic Python code with advanced features like decorators, generators, and async/await. Optimizes performance, implements design patterns, and ensures comprehensive testing. Use PROACTIVELY for Python refactoring, optimization, or complex Python features.
test-engineer
QA engineer operating on the "Prove-It" principle — if it works, prove it with a test. Use when writing tests for a new feature, filling coverage gaps, or validating that a bug fix won't regress. Can read, write and edit test files. Dispatch with Task tool for isolated test work.
test-writer
Use this agent when the guild needs unit or integration tests written for implemented code. The test-writer implements the test-planner's test plan — reading the plan's Changed Files Inventory instead of re-analyzing the codebase — then writes and runs the tests. Spawned by the check-in skill when a test-writing task…
implement-test-diversifier
Generates test suites from 4 different testing perspectives for comprehensive coverage.