Borrowing it
Nothing to install: this file belongs to hs737/mcp-server-for-ynab. 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/hs737/mcp-server-for-ynab/master/.agents/skills/architecture-boundaries/SKILL.mdgit clone --depth 1 https://github.com/hs737/mcp-server-for-ynabWrote 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/skills/hs737/mcp-server-for-ynab/architecture-boundaries)<a href="https://agentmods.dev/skills/hs737/mcp-server-for-ynab/architecture-boundaries"><img src="https://agentmods.dev/badge/skills/hs737/mcp-server-for-ynab/architecture-boundaries/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/skills/hs737/mcp-server-for-ynab/architecture-boundaries"><img src="https://agentmods.dev/badge/skills/hs737/mcp-server-for-ynab/architecture-boundaries.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 | $0.00028 | $0.00695 |
| Opus 5 | $0.00014 | $0.00347 |
| Sonnet 5 | $0.00006 | $0.00139 |
| Haiku 4.5 | $0.00003 | $0.00069 |
Grade A, and why
architecture-boundaries 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 10d 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 — 68 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Architecture Boundaries
Use this skill when adding or changing core logic, MCP tools, HTTP APIs, jobs, integrations, or runtime orchestration in this Python repository.
Use When
- Adding MCP tools, resources, or prompts
- Adding HTTP routes (if any)
- Adding orchestration or business logic
- Adding database access patterns
- Adding jobs, workers, or scheduled tasks
- Adding third-party integrations (for example YNAB API clients)
- Reviewing whether a change belongs in the right layer
Read First
AGENTS.md(if present)README.mdpyproject.toml(package layout, entry points)- Any repo-specific architecture docs (for example
docs/architecture.md,docs/current-state.md)
Core Rules
- Transport / protocol layer (MCP server setup, FastAPI routers, CLI entrypoints) owns wiring, validation at the boundary, and mapping to/from wire types—not core business rules.
- Services or domain modules own workflows, state transitions, and business rules.
- Data access owns persistence and queries, not business policy.
- Integration clients (YNAB SDK, HTTP clients) own provider-specific IO and normalization, not app-wide orchestration.
- MCP tool handlers should stay thin: parse inputs, call services, map errors to structured tool results. Do not hide durable invariants only in tool docstrings or prompts.
- Do not invent a parallel architecture when the repo already has one; follow existing package layout (
src/layout, module naming). - Keep boundaries obvious enough that future agents can place code correctly.
- Multi-step workflows: Reusable step logic belongs in domain or service modules, not duplicated in each tool or route.
- Persistence: Prefer normalized storage and explicit fields as source of truth. Use
data-access-disciplinefor schema and transactions.
Typical Python layout (adapt to this repo)
| Layer | Examples |
|---|---|
| Entry | __main__.py, server.py, Typer/Click CLI, FastAPI APIRouter |
| MCP surface | Tool/resource registration; argument validation via Pydantic |
| Services | services/, domain/, use-case functions |
| Integrations | clients/ynab.py, thin wrappers around external APIs |
| Persistence | db/, repositories, SQLAlchemy models (if used) |
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.
- 10d ago First seen · 68 lines · 28 tokens per session scan A a13223dd3002
architecture-boundaries is a skill published in the GitHub repository hs737/mcp-server-for-ynab (1 stars, last pushed 2d ago), licensed Apache-2.0. It adds 28 tokens to every session and 695 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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