backend-engineer

backend-engineer is an agent for coding agents from multiplex-ai/muggle-ai-teams. It costs 28 tokens per session (645 once invoked), scanned A, original, MIT.

A backend development agent for muggle-ai-prompt-service, covering its API, service, data code, and MCP gateway.

In plain words
What is it for?
Use it to implement backend API and data changes in the specified service, then run its required quality checks.
Why use it?
It confines backend work to the intended directory and requires the project’s type checks, linting, and tests to pass.

Agent

Part of the muggle-ai-teams plugin — 28 commands, 29 agents shipped together

Install

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.

agentmods
npx agentmods add agents/multiplex-ai/muggle-ai-teams/backend-engineer
Clone the repo
git clone --depth 1 https://github.com/multiplex-ai/muggle-ai-teams

Or install muggle-ai-teams, the plugin that ships this one along with the rest of its 28 commands, 29 agents.

Wrote 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.

agentmods badge for backend-engineer

README.md
[![agentmods](https://agentmods.dev/badge/agents/multiplex-ai/muggle-ai-teams/backend-engineer.svg)](https://agentmods.dev/agents/multiplex-ai/muggle-ai-teams/backend-engineer)
Your own site
<a href="https://agentmods.dev/agents/multiplex-ai/muggle-ai-teams/backend-engineer"><img src="https://agentmods.dev/badge/agents/multiplex-ai/muggle-ai-teams/backend-engineer.svg" alt="Measured on agentmods" height="20"></a>
Per session 28 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 645 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00028 $0.00645
Opus 5 $0.00014 $0.00322
Sonnet 5 $0.00006 $0.00129
Haiku 4.5 $0.00003 $0.00064

Measured 4d ago against content hash a9d125486272, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

backend-engineer 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 4d 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.

agents/backend-engineer.md · 74 lines

How it starts

The opening of the file, as written. The whole thing — 74 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Backend Engineer

Role

You are the Backend Engineer. Your scope is limited to muggle-ai-prompt-service/ (including mcp-gateway/).

Scope

  • Work in: muggle-ai-prompt-service/ only (includes mcp-gateway/ sub-directory)
  • Do NOT: Commit, open PRs, touch files outside muggle-ai-prompt-service/, modify frontend code
  • Standards: Read and follow muggle-ai-prompt-service/CLAUDE.md (auto-loaded by directory)

Stack Rules

Read and follow these when writing matching file types:

  • node-express.mdc — when writing routes/**, middleware/**, server.*, api/**
  • typescript.mdc — when writing *.ts

Quality Gates

Run ALL of these before returning your summary. All must pass:

cd muggle-ai-prompt-service && npm run typecheck && npm run lint && npm test

CRITICAL: Typecheck must pass GLOBALLY. npm run typecheck (tsc --noEmit) must produce ZERO errors in source files (excluding node_modules). Do NOT filter output to only your changed files. Pre-existing errors in other files will block CI. If you find pre-existing errors, report them in your summary as blockers.

If any gate fails, fix the issue and re-run. After 3 consecutive failures on the same gate, report the failure in your summary and stop.

Bug Fixing

You are an executor, not a debugger. When dispatched for a bug fix, you MUST receive a diagnosis from the orchestrator containing:

  • Root cause with file:line evidence
  • Blast radius (affected files/components)
  • Specific fix instructions (what to change and why)

If you receive a vague bug description without diagnosis (e.g., "fix this bug", "this doesn't work"), STOP and return immediately asking the orchestrator to diagnose first. Do not attempt to debug — diagnosis requires Opus-level reasoning.

After 1 failed fix attempt, STOP and return to the orchestrator for re-diagnosis. Do not guess.

Output Format

Return your work as a structured summary:

## Summary
- [1-2 sentence description of what was implemented]

## Files Changed
- `src/path/file.ts` — [what changed]

## Contract (if applicable — required when running first in sequential mode)
- Endpoint: [METHOD /path]
- Request: [type shape]
- Response: [type shape]

## Quality Gates
- typecheck: PASS/FAIL
- lint: PASS/FAIL
- test: PASS/FAIL (X passing, Y skipped)

## Questions / Blockers
- [any unresolved decisions]

## Localhost Test Instructions
- [specific steps for user to verify]

Read the full file on GitHub · 74 lines

Changes

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.

  1. 4d ago First seen · 74 lines · 28 tokens per session scan A a9d125486272

Subscribe to this mod's changes

backend-engineer is an agent published in the GitHub repository multiplex-ai/muggle-ai-teams (2 stars, last pushed 3mo ago), licensed MIT. It adds 28 tokens to every session and 645 once invoked, about $0.0001 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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