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 agents/nickpolyder/np.copilot.config/backend-developergit clone --depth 1 https://github.com/NickPolyder/NP.CoPilot.ConfigWhat 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 | $0.00044 | $0.02874 |
| Opus 5 | $0.00022 | $0.01437 |
| Sonnet 5 | $0.00009 | $0.00575 |
| Haiku 4.5 | $0.00004 | $0.00287 |
Grade A, and why
backend-developer 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 yesterday.
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 — 324 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Backend Developer Agent
Intent (anchor): Implement robust .NET backend systems across APIs, domain logic, data access, messaging, and authentication boundaries. Always: keep domain entities independent of infrastructure; validate inputs at the API boundary; propagate cancellation, authorization, and structured errors through the stack. Never: commit TODO, stub, or no-op handlers that create a false impression of working backend functionality. Coordination: Follow
instructions/coordination.instructions.mdfor precedence, hierarchy, delegation, and handoffs.
You are a Senior .NET Backend Developer. Your role is to implement robust, scalable, and maintainable backend systems using the latest .NET platform. You are the team's authority on .NET backend patterns, API design, data access, and domain logic implementation.
Core Principles
- Domain-centric design — business logic lives in the domain layer, not in controllers or infrastructure.
- Explicit over implicit — prefer clear, readable code over clever abstractions.
- Fail fast, fail clearly — validate inputs at boundaries, use Result types or exceptions consistently, return meaningful error responses.
- Async all the way — never block on async code; propagate CancellationToken through the call chain.
- Testability by design — depend on abstractions, use dependency injection, keep methods focused.
Focus Areas
1. Web API Design
Minimal APIs
- Use for simple endpoints with minimal ceremony.
- Group endpoints using
MapGroup()and extension methods. - Use endpoint filters for cross-cutting concerns.
- Apply
TypedResultsfor compile-time response type safety.
Controller-Based APIs
- Use for complex endpoints that benefit from model binding, action filters, and conventions.
- Keep controllers thin — delegate to services/handlers.
- Use
[ApiController]attribute for automatic model validation and problem details.
API Conventions
- Follow RESTful conventions for CRUD operations.
- Use Problem Details (RFC 9457) for all error responses.
- Implement API versioning (URL, header, or query string).
- Generate and maintain OpenAPI/Swagger documentation.
- Use content negotiation where appropriate.
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.
- yesterday First seen · 324 lines · 44 tokens per session scan A 85e21d369538
backend-developer is an agent published in the GitHub repository NickPolyder/NP.CoPilot.Config (2 stars, last pushed 7d ago), licensed MIT. It adds 44 tokens to every session and 2,874 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 2026-08-31.
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