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 skills add sandeepmvl/rails-skills --skill 40-when-not-to-use-microservicesgit clone --depth 1 https://github.com/sandeepmvl/rails-skillsWrote 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/sandeepmvl/rails-skills/40-when-not-to-use-microservices)<a href="https://agentmods.dev/skills/sandeepmvl/rails-skills/40-when-not-to-use-microservices"><img src="https://agentmods.dev/badge/skills/sandeepmvl/rails-skills/40-when-not-to-use-microservices/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/sandeepmvl/rails-skills/40-when-not-to-use-microservices"><img src="https://agentmods.dev/badge/skills/sandeepmvl/rails-skills/40-when-not-to-use-microservices.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 | $0.00129 | $0.02282 |
| Opus 5 | $0.00064 | $0.01141 |
| Sonnet 5 | $0.00026 | $0.00456 |
| Haiku 4.5 | $0.00013 | $0.00228 |
Grade A, and why
when-NOT-to-use-microservices 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 12d 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 — 184 lines — stays where its author put it; the contents beside it link to each section on GitHub.
When NOT to Use Microservices
Most teams who adopt microservices regret it. The complexity tax is real, the velocity gain is theoretical, and a well-organized Rails monolith scales further than you think. This skill exists to slow the user down before they make an architecturally expensive mistake.
The opinion
Stay on the monolith. Default to a modular monolith with clear domain boundaries (use packs, namespaces, and engines if needed). Microservices are a solution to organizational problems — too many teams stepping on each other — not to scaling problems. If you have fewer than ~50 engineers, you do not have an organizational problem big enough to justify the distributed-systems tax.
This isn't dogma. It's a hard-earned consensus across the industry: GitHub, Basecamp, Shopify, and Stack Overflow all run mostly-monolith Rails. Companies that went micro and walked it back: Segment, Istio (kind of), InVision, Amazon Prime Video (2023 — went monolith, cut costs 90%).
The microservices tax (what you're paying for)
When you split, you take on:
- Network failure modes. Every in-process call becomes a network call. Timeouts, retries, circuit breakers, partial failures.
- Distributed transactions. ACID across services is impossible. You get sagas, eventual consistency, or compensating transactions — all of which leak abstraction.
- Cross-service debugging. A bug crosses 4 services. Logs are in 4 places. You need distributed tracing (see
distributed-tracing-rails) just to follow a request. - Schema coupling, just different. "We decoupled the database!" Yes — and now you have eventual consistency, dual-writes, and outbox patterns to keep things in sync.
- Deploy choreography. You add a column → 3 services need redeploy. Backward-compatible API versioning becomes mandatory.
- Multiplied infrastructure. Each service needs CI, CD, monitoring, alerting, on-call rotation, security scans, dependency updates, runbook docs.
- Talent tax. Senior engineers who understand distributed systems are 2-3x more expensive. Junior engineers can't safely ship across service boundaries.
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 12d ago First seen · 184 lines · 129 tokens per session scan A 6f06b72c057d
when-NOT-to-use-microservices is a skill published in the GitHub repository sandeepmvl/rails-skills (21 stars, last pushed 3mo ago), licensed MIT. It adds 129 tokens to every session and 2,282 once invoked, about $0.0006 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.
Other skills, from other repositories
mem0-oss-to-platform
Plan and then execute a migration of a project from the mem0 open-source / self-hosted SDK (the local Memory class) to the mem0 Platform / hosted / managed SDK (the MemoryClient class). Use this whenever a developer wants to move, switch, or migrate their mem0 usage off OSS/self-hosted to the hosted API — e.g.…
agui-dotnet-protobuf
Use the protobuf wire transport (instead of the default Server-Sent Events) for an AG-UI connection with the AG-UI .NET SDK — a compact binary event stream negotiated via the Accept header. USE FOR: making an AGUIChatClient prefer protobuf by wiring an AGUIEventStreamHandler with ProtobufEventStreamFormatter (then…
azure-mgmt-botservice-dotnet
Azure Resource Manager SDK for Bot Service in .NET. Management plane operations for creating and managing Azure Bot resources, channels (Teams, DirectLine, Slack), and connection settings. Triggers: "Bot Service", "BotResource", "Azure Bot", "DirectLine channel", "Teams channel", "bot management .NET", "create bot".
fastapi-router-py
Create FastAPI routers with CRUD operations, authentication dependencies, and proper response models. Use when building REST API endpoints, creating new routes, implementing CRUD operations, or adding authenticated endpoints in FastAPI applications.
aws-sdk-java-v2-core
Provides AWS SDK for Java 2.x client configuration, credential resolution, HTTP client tuning, timeout, retry, and testing patterns. Use when creating or hardening AWS service clients, wiring Spring Boot beans, debugging auth or region issues, or choosing sync vs async SDK usage.
migrate-segw-to-rap
Reverse-engineer a SEGW-built OData V2 service (MPC/DPC/MPCEXT/DPCEXT) into a modern RAP V4 service — tables, CDS views (interface + projection), behavior definitions, draft entities, service definition + binding. Use when asked to "migrate this SEGW service to RAP", "convert OData V2 to V4 RAP", "modernize this…