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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: counts are per-day, capped at 90 days, include a current-month rollup, and are 'updated through the day' (freshness/latency disclosure). Missing auth or rate-limit notes keeps it from a 5.

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 tight sentences with zero filler; the primary output (daily counts) is front-loaded before the secondary rollup and the freshness caveat.

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?

For a 2-parameter read-only tool with no output schema, the description adequately conveys what comes back (per-day counts plus a monthly total) and its currency. It stops short of describing the shape of the returned series, but nothing critical to correct invocation is missing.

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 coverage is 100%, with the days parameter already documenting range 1-90 and default 30, so the description mostly restates what the schema provides ('last 30 days (up to 90)'). Baseline 3 is appropriate given the schema does the heavy lifting.

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 and resource ('Returns how many messages a project has sent') with explicit scope (per day, last 30 days up to 90, plus current calendar month total). This clearly separates it from siblings like get_project_settings and list_flagged_messages.

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?

Usage is implied by the metric it returns, but there is no explicit when-to-use guidance, no exclusion of alternatives, and no prerequisite or permission information. An agent must infer that this is the tool for volume/throughput questions.

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