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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower. The description adds genuinely non-obvious domain behavior: amounts are bare numbers with no currency, and a prerequisite call is required before reporting a currency. It does not additionally note auto-pagination, but that is already in the schema.

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, no padding, and the currency caveat is placed where it will be read before the agent reports figures. Every sentence carries distinct information.

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?

With no output schema, the description usefully compensates by disclosing the currency ambiguity in returned amounts. It does not describe the fields a snapshot contains, but for a simple list tool over fully-documented params this is close to complete.

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% across all three parameters, so the schema already carries param meaning. The description only adds interpretive value for project_id (trends over time); page/per_page semantics come entirely from the schema. Baseline 3 fits.

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 ('List historical cost snapshots for projects') and adds scope ('historical', 'trends over time') that distinguishes it conceptually from the singular get_project_cost_snapshot sibling. It stops short of explicitly naming that sibling or saying it returns the collection rather than one snapshot.

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 usage pattern ('Filter by project_id to see cost trends over time') and, notably, routes the agent to another tool ('call get_organization_settings for currency_code before stating one'). It does not name when to use this over get_project_cost_snapshot, but the use context is clear.

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