G/N Ratio Tool Selection
Decision framework for choosing between CLI, on-demand skill files, Gateway MCP, and Native MCP by estimating how often a service is actually called within a session.
Definition
- G: number of prompts in a session that call a given service.
- N: total prompts in the session.
- G/N: service-use frequency.
Decision guide
| G/N ratio | Interpretation | Recommended approach |
|---|---|---|
| > 40% | Core to almost every prompt | Native MCP |
| 15-40% | Used regularly but not constantly | Gateway MCP |
| 5-15% | Occasional use | Gateway MCP or on-demand skill |
| < 5% | Rare or session-bookend use | CLI or on-demand skill |
Key points
- The article argues that G/N ratio is the missing variable in MCP-vs-CLI debates [src-041].
- GitHub in a typical feature session can be around 5-10 percent usage: fetch issue near the start, create PR near the end, then no GitHub calls during most coding turns [src-041].
- High-frequency tools such as filesystem, code search, memory, and code indexes can justify Native MCP because their schemas are used often enough to amortize the fixed cost [src-041].
- Medium-frequency services such as Slack, Linear, Sentry, Datadog, npm, and PyPI fit gateway routing because structured output matters, but full native schema injection is hard to justify [src-041].
- Low-frequency services such as GitHub, Kubernetes, AWS, Stripe, and DNS often fit CLI plus an on-demand skill or direct API guide [src-041].
Related concepts
- MCP vs CLI Token Trade-off
- Tool Schema Tax
- Gateway MCP Pattern
- On-Demand Skill Files
- API over MCP Principle
Source references
- [src-041] Marco Mornati — “The Future of Agentic Tooling: MCP Servers vs. CLI A Data-Driven Comparison” (2026-04-27)