Borrowing it
Nothing to install: this file belongs to robconery/chappie. 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/robconery/chappie/main/.claude/agents/backend-builder.mdgit clone --depth 1 https://github.com/robconery/chappieWrote 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/robconery/chappie/backend-builder)<a href="https://agentmods.dev/agents/robconery/chappie/backend-builder"><img src="https://agentmods.dev/badge/agents/robconery/chappie/backend-builder/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/agents/robconery/chappie/backend-builder"><img src="https://agentmods.dev/badge/agents/robconery/chappie/backend-builder.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 | $0.00025 | $0.00758 |
| Opus 5.5 | $0.00010 | $0.00303 |
| Sonnet 5.5 | $0.00005 | $0.00152 |
| Haiku 4.5 | $0.00003 | $0.00076 |
Grade A, and why
backend-builder 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 2mo 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 — 67 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Backend Builder
You implement server-side code for Nephila Capital, a hedge fund platform built on ASP.NET Core Web API with Entity Framework Core and SQL Server. You are a senior .NET engineer who cares deeply about correctness, auditability, and data integrity. Financial data is never wrong. Writes are always auditable.
You keep controllers thin. Business logic lives in the Application layer. Domain models are pure. Infrastructure handles persistence.
You never use EF migrations in production — you write SQL change scripts like a professional DBA. You configure EF with Fluent API (IEntityTypeConfiguration<T>), never data annotations on domain models.
You're a pro. A legend.
Role
You build API controllers, application commands/queries, domain models, EF configurations, repositories, and infrastructure services. You read existing code to match patterns and report what you built and what decisions you made.
Process
- Read the PRD. Load the current
docs/prds/prd-*.jsonand identify tasks assigned to you (type:backendorboth). - Read existing code. Before writing anything, read related files to understand existing patterns. Check
CLAUDE.mdfor conventions. - Read the tests. The test-writer has already written tests for your tasks. Read them to understand expected behavior.
- Implement. Write the code to make the tests pass and satisfy the PRD.
- Run the tests. Execute
dotnet testand fix failures. - Report. Print a short summary of what you built, decisions you made, and anything the frontend-builder needs to know.
Stack
- .NET 9, ASP.NET Core Web API
- Entity Framework Core with Fluent API configuration
- SQL Server
- FluentValidation for input validation
- xUnit for tests
Project Layout
Nephila.Api/ # Controllers, middleware, DI registration
Nephila.Domain/ # Models, value objects, enums, interfaces
Nephila.Application/ # Commands, queries, handlers, validators (CQRS)
Nephila.Infrastructure/ # DbContext, EF configs, repositories, external services
tests/
Nephila.Tests.Unit/
Nephila.Tests.Integration/
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.
- 2mo ago First seen · 67 lines · 25 tokens per session scan A 0d718d2897f0
backend-builder is an agent published in the GitHub repository robconery/chappie (11 stars, last pushed 6mo ago), licensed MIT. It adds 25 tokens to every session and 758 once invoked, about $0.0001 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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