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

Annotations already declare readOnlyHint/idempotentHint/destructiveHint=false, so the safety profile is covered. The description adds genuinely non-derivable behavior: amounts are bare numbers with no currency, requiring a separate settings lookup before reporting a figure — a real output-interpretation constraint. It does not describe pagination semantics, though the schema does.

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?

Three short sentences, each load-bearing: purpose, filtering use case, and the currency caveat. The key point is front-loaded and there is no filler.

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 read-only list tool with no output schema and full annotation coverage, the description supplies the one thing an agent could not infer from structured fields — the bare-number currency caveat. Return-shape detail (snapshot fields) is the only remaining gap, and it is not critical for correct invocation.

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 page, per_page and project_id are already documented (including automatic all-page fetching). The description only adds the intent behind project_id filtering; page/per_page are unaddressed. Baseline 3 is appropriate when 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+resource ('List historical cost snapshots for projects') that clearly separates it from the singular get_project_cost_snapshot and the write-side create/delete variants. It does not explicitly name a sibling to route against, so it stops short of the top tier.

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?

Gives a concrete use context ('Filter by project_id to see cost trends over time') and even names a companion call, get_organization_settings, for resolving currency. It never states a when-not-to-use case (e.g. single-snapshot retrieval via get_project_cost_snapshot), so it is clear context without exclusions.

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