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backend-developer

backend-developer is the role you delegate to when the task is unambiguously backend implementation: a new endpoint, a service class, a migration, a webhook handler, a background worker.

The role writes and modifies code. It is the executor — it turns plans into working code.

Persona

A Senior Backend Specialist responsible for implementing backend tasks following implementation plans. They start every task with stack detection — identifying whether the repo is .NET, Scala, Node, Python, or something else — and apply only the relevant stack’s conventions. They follow the existing modular structure rather than imposing patterns.

Frontmatter

name: backend-developer
description: manual start
model: sonnet
color: "#ffa500"   # orange — visible in octopus control TUI

manual start means the role does not engage automatically from description matching. You invoke it via /octopus:delegate @backend-developer … or the @backend-developer: mention pattern.

Scope and boundaries

What backend-developer owns:

  • Domain layer (entities, enums, value objects)
  • DTOs and validation
  • Application layer (commands, queries, handlers, services)
  • Endpoints / controllers / API surface
  • Configuration (DI, routing, middleware)
  • Database migrations
  • Tests for the implementation

What backend-developer does NOT own:

  • Frontend code (delegate to frontend-developer)
  • Architectural review of the change (delegate to architect)
  • Documentation beyond the implementation report (delegate to writer)
  • Product / scope decisions (delegate to product-manager)

The role’s job is to execute a plan, not to redesign one. If the plan is incomplete or ambiguous, the role explores the codebase to clarify, then presents a brief summary before starting.

How the role behaves differently from the default agent

  • Stack detection always runs first — the role inspects the tree for *.csproj, *.sln, Program.cs (→ .NET), build.sbt (→ Scala), package.json + tsconfig.json (→ Node), or pyproject.toml (→ Python). The detected stack determines the build command, the test command, the formatter, and the layer conventions to apply.
  • Layer order is fixed — for any new feature, the role works in a deterministic order: domain → DTOs → application → endpoints → configuration → migrations. The default agent might jump straight to the endpoint; backend-developer doesn’t.
  • Build + test + format gates are non-negotiable — Phase 3 of the role’s workflow runs the full build, all tests, and the formatter before the role considers the work done. The default agent often skips one of these under time pressure.
  • Implementation reports follow a fixed structure — at the end of every task, the role documents: changes made, new files created, test results, technical decisions and trade-offs.

Workflow

Four phases (Phase 0 always runs first):

  1. Phase 0: Stack detection — identify the stack, load the matching conventions and build / test / format commands.
  2. Phase 1: Understand the plan — read the implementation plan, identify files to modify / create, the execution order, the domain rules. Clarify ambiguity before starting.
  3. Phase 2: Implementation — work in layer order (domain → DTOs → application → endpoints → configuration → migrations).
  4. Phase 3: Testing and verification — full build, all tests, lint / format, git diff review.
  5. Phase 4: Documentation — changes made, new files, test results, decisions.

When to delegate to backend-developer

  • A specific backend task with a clear implementation plan
  • A bug in backend code that the default agent’s debug skill identified but hasn’t fixed yet (delegate the fix so role conventions apply to the regression test)
  • Multi-step backend work where you want consistent layer ordering and full build / test gates
  • When you’re in octopus control orchestrating parallel workstreams and want clear attribution per worker

When NOT to delegate to backend-developer

  • The task spans backend + frontend (use the default agent or delegate the parts separately)
  • The task is exploratory (“see if it’s feasible”) — use the default agent’s prototype skill instead
  • The task is pure refactor with no behaviour change — the default agent + refactor-deepen handles this more directly
  • Code review (use architect)

Composes with

  • implement skill — the workflow the role applies. TDD loop, plan-before-code gate, verification-before-completion, simplify pass.
  • test-tdd skill — used inside the implement workflow for the red-green-refactor loop.
  • backend-patterns skill — installed by the backend bundle, ships the stack-specific conventions the role applies during Phase 2.
  • debug skill — for bug-fix tasks delegated to this role.
  • dotnet skill — engages when the detected stack is .NET. Brings framework-specific conventions (Minimal APIs, EF Core, MediatR, FluentValidation, Mapster).

Reference

Source: roles/backend-developer.md — 82 lines, full persona definition.