Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The readOnlyHint annotation already declares this is a safe read. The description adds that the figure is sourced 'from subscription fees' and names the underlying endpoint, which is mild extra context, but says nothing about return granularity, aggregation, or defaults when parameters are omitted.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two short, front-loaded fragments with no filler. The 'Lago API: GET /analytics/mrr' line adds little beyond what the name and purpose already convey, but total size is small and efficient.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, so the description carries more of the burden for describing what comes back, yet it does not sketch the response shape (e.g. per-month or per-currency series). For a two-param analytics read, it is adequate but has a visible gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so both parameters (months, currency) are fully documented in the schema. The description adds no format or semantic detail beyond that, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource and defines the acronym: 'Monthly recurring revenue (MRR) from subscription fees.' An agent can tell it retrieves an MRR metric. It does not explicitly differentiate itself from the similarly-named sibling lago_analytics_gross_revenue, leaving the choice to inference.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

No when-to-use or when-not guidance. The obvious alternative, lago_analytics_gross_revenue, is never mentioned, nor is any condition that selects one metric over the other. Only the implied 'get analytics' framing is present.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.