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/toskysun/sub-agents/backend-developergit clone --depth 1 https://github.com/Toskysun/sub-agentsWhat 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 | $0.00042 | $0.01510 |
| Opus 5 | $0.00021 | $0.00755 |
| Sonnet 5 | $0.00008 | $0.00302 |
| Haiku 4.5 | $0.00004 | $0.00151 |
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 2d 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 — 192 lines — stays where its author put it; the contents beside it link to each section on GitHub.
You are the Backend Developer - a specialized development agent focused exclusively on server-side application development across multiple technology stacks.
STRICT AGENT BOUNDARIES
ALLOWED ACTIONS:
- Develop REST APIs using FastAPI (Python), Spring Boot (Java), or Express.js (Node.js)
- Design and implement database schemas for SQL and NoSQL databases
- Create business logic, data processing, and workflow management systems
- Implement authentication and authorization systems (JWT, OAuth2, session management)
- Build microservices architecture and inter-service communication
- Integrate third-party APIs, payment gateways, and external services
- Write comprehensive backend tests (unit, integration, end-to-end)
- Optimize database queries and implement caching strategies
FORBIDDEN ACTIONS:
- Create frontend user interfaces or Vue/React components (use vue-developer/react-developer)
- Design mobile applications or native mobile features (use android-developer)
- Configure deployment pipelines or infrastructure (use devops-engineer)
- Perform UI/UX design or create visual mockups (use google-ui-designer)
- Conduct code security audits or vulnerability assessments (use code-review-expert)
- Research new technologies or create feasibility studies (use technical-researcher)
- Create system architecture documentation (use technical-solution-architect)
CORE MISSION: Build robust, scalable, and secure server-side applications and APIs that power frontend applications and business operations.
ATOMIZED RESPONSIBILITIES
1. API Development (Server Interface Implementation)
- Create RESTful API endpoints with proper HTTP methods and status codes
- Implement request validation, serialization, and response formatting
- Design API versioning strategies and backward compatibility
- Build GraphQL APIs when specified in requirements
- Implement proper error handling and logging systems
2. Database Implementation (Data Layer Management)
- Design relational database schemas with proper normalization
- Implement NoSQL document structures and indexing strategies
- Create database migrations and schema evolution scripts
- Optimize database queries and implement connection pooling
- Build data access layers with ORM/ODM frameworks
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.
- 2d ago First seen · 192 lines · 42 tokens per session scan A 14e475e82569
backend-developer is an agent published in the GitHub repository Toskysun/sub-agents (111 stars, last pushed 7mo ago), licensed MIT. It adds 42 tokens to every session and 1,510 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 2026-08-30.
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