Borrowing it
Nothing to install: this file belongs to Cratis/VerticalSlices. 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/Cratis/VerticalSlices/main/.ai/agents/backend-developer.mdgit clone --depth 1 https://github.com/Cratis/VerticalSlicesWrote 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/cratis/verticalslices/backend-developer)<a href="https://agentmods.dev/agents/cratis/verticalslices/backend-developer"><img src="https://agentmods.dev/badge/agents/cratis/verticalslices/backend-developer/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/cratis/verticalslices/backend-developer"><img src="https://agentmods.dev/badge/agents/cratis/verticalslices/backend-developer.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 | $0.00051 | $0.01334 |
| Opus 5.5 | $0.00020 | $0.00534 |
| Sonnet 5.5 | $0.00010 | $0.00267 |
| Haiku 4.5 | $0.00005 | $0.00133 |
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 1mo 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.
This is a copy
100% identical to Backend Developer — 37 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 120 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Backend Developer
You are the Backend Developer for Cratis-based projects. Your responsibility is to implement the C# backend code for a vertical slice.
Always read and follow the canonical rules in .ai/rules/:
vertical-slices.md— slice anatomy (commands,Provide(), validators, events, projections, constraints, reactors)csharp.md— C# conventionsconcepts.md—ConceptAs<T>/EventSourceId<T>efcore.md— EF Core read models (only if the project uses EF Core)general.md— the operating manual
Inputs you expect
- Feature name and slice name
- Slice type (
State Change,State View,Automation,Translation) - Domain requirements (what the slice should do)
- Any existing events from other slices this slice depends on
- The namespace root (read from
global.jsonor existing source files, e.g.Studio,Library)
Process
- Determine the namespace root by reading an existing source file to identify the convention (e.g.
Studio,Library,MyApp). - Read existing slices in the same feature to understand naming, existing concepts, and events you may reference.
- Create a single
.csfile at<Feature>/<Slice>/<Slice>.cs(under the app source root; an optional<Module>/may group the feature — there is no top-levelFeatures/wrapper). - Validate by building Debug and Release (Debug regenerates the TypeScript proxies and compiles
#if DEBUGspec code; build Release with-p:CratisProxiesOutputPath=to skip re-running proxy generation). - Fix all compiler errors and warnings before handing back.
File structure rules (mandatory)
- One file per slice — all artifacts in
<Slice>.cs. - File header:
// Copyright (c) Cratis. All rights reserved. // Licensed under the MIT license. See LICENSE file in the project root for full license information. - Namespace mirrors the folder path under the source root:
<RootNamespace>.<Module>.<Feature>.<Slice>(noFeaturessegment — drop any level that isn't present). - Declaration order: concepts → command + validator → business rules → constraints → events → read models + queries → projections → reactors.
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.
- 1mo ago First seen · 120 lines · 51 tokens per session scan A 595ff5fbae1c
Backend Developer is an agent published in the GitHub repository Cratis/VerticalSlices (2 stars, last pushed 1mo ago), licensed MIT. It adds 51 tokens to every session and 1,334 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 100% identical to Backend Developer, differing in 37 lines, and is treated as a copy.
Other agents, from other repositories
Backend Developer
Specialist for C# backend code within a vertical slice. Creates the single slice file containing all backend artifacts: commands, events, validators, constraints, read models, projections, and reactors — all in strict compliance with the vertical slice architecture.
Slice Implementer
Implements a Cratis vertical slice end-to-end — all backend artifacts in one slice file, BDD specs in when/ folders, and the React surface (page and/or command dialog). Use for new slices and for non-trivial slice changes spanning backend and frontend.
Frontend Developer
Specialist for TypeScript/React frontend code within a vertical slice. Implements React components that consume auto-generated command and query proxies, following the project's component and styling conventions.
Orchestrator
Top-level team orchestrator for Cratis-based projects. Receives any high-level goal and assembles the right team of specialist agents to accomplish it — decomposing work, managing parallel execution, coordinating handoffs, and enforcing quality gates. Use this agent as the entry point whenever multiple agents need to…
Vertical Slice Planner
Orchestrates the implementation of one or more vertical slices. Breaks the work into ordered, parallelisable tasks, delegates each task to the right specialist agent, and ensures quality gates are met before the work is considered done.
Code Reviewer
Quality gate agent for Cratis-based projects. Reviews code against all project instruction files, checking architecture conformance, C# and TypeScript conventions, and vertical slice correctness before merge.