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

Source references

  • [src-041] Marco Mornati — "The Future of Agentic Tooling: MCP Servers vs. CLI A Data-Driven Comparison" (2026-04-27)

Robin Cartier perspective

This page is part of Robin Cartier's working AI knowledge graph: a practical research layer for production AI, recommendation systems, experimentation, GEO, and agentic web readiness.

The useful next step is to connect this concept back to applied product leadership and operating models.

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Keep reading from this thread

From 500 indexed pages and articles.

  1. Wiki concept Tool Schema Tax The fixed context cost paid when an agent runtime injects tool schemas into every prompt, regardless of whether those tools are used in Related by 041
  2. Wiki concept On-Demand Skill Files Pattern for keeping service-specific CLI/API guidance out of the always-loaded project context until the agent actually needs that service. Related by 041
  3. Wiki concept Gateway MCP Pattern Tool-access architecture where the agent sees one small MCP router while backend service schemas are loaded or invoked lazily. Related by 041