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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower; the description adds genuinely useful behavior by disclosing that the ladder starts from data already used this period (a proration/continuation semantic) and that this is the account rate, not the public shelf. It does not mention return shape beyond the volume-points case, but that is a minor gap.

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, front-loaded with what is returned, then the scoping caveat, then the parameter behavior. No filler; every sentence carries 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?

For a two-parameter read-only lookup with no output schema, the description covers what is returned, the scope of the rate, and the effect of omitting gb. Only the shape of the returned ladder points is left implicit, which is a small remaining 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 coverage is 100%, so the baseline is 3, but the description earns an extra point by explaining the consequence of omitting gb ('returns the volume points') — something the schema's 'Omit when they have not said' does not state. That is real meaning added beyond the structured field.

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 the customer's pay-as-you-go data ladder — and draws a real conceptual boundary against the 'public shelf' rate, which is the distinction an agent needs to avoid confusing it with the quote_* / get_did_rate siblings. It stops short of naming an actual sibling tool, so it is clear but not fully differentiated.

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: fetch this when you need the account-specific rate rather than a public quote. The description supplies the gb-omission rule, which is a calling condition, but it never states when to prefer this over quote_number/quote_esim/get_did_rate, nor any prerequisites. Minimum-viable guidance.

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