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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the description earns credit for adding what they don't cover: the required role (owner, admin or finance) and the fact that results include a hypothetical approval projection plus per-provider reporting coverage. It doesn't mention cost or latency of the projection, keeping 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?

One dense sentence that front-loads the resource and period before the two modes and the permission requirement. Every clause carries information; it is slightly overloaded but not padded.

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 an output schema covering return shape and annotations covering safety, the remaining gaps an agent needs — period format, the two content modes, provider-coverage signal, and the role requirement — are all present. Nothing essential to calling it correctly 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 description coverage is 0%, so the description must compensate; it does partially by restating the period as a YYYY-MM month, which explains the meaning behind the pattern. It adds no detail on whether period must fall in the past or how the hypothetical projection is selected relative to a period.

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?

The description names the resource (a month's journal entries for AI costs) and the scope (a single YYYY-MM period), and distinguishes the two content modes: settled approved/frozen entries versus a hypothetical projection. It never states the retrieval verb explicitly and does not name a sibling, so it stops short of a 5.

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?

"Needs an owner, admin or finance member" gives a real prerequisite, and the approved-vs-hypothetical framing implies when the tool is useful. However, it never states when to prefer this over siblings like approve_month or reconciliation_status, so the when-to-use guidance is only implied.

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