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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds real behavioral context beyond that: it discloses the depth and shape of the payload ('every energy-charge tier... 12x24 month-by-hour period schedules'), which tells the agent this is a large, single-record fetch rather than a list. It does not mention failure behavior for an invalid label or the DEMO_KEY throttle beyond what the schema already says.

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 sentences, front-loaded with the verb and a compact enumeration of the returned structure. The long field list is justified because there is no output schema, though the sentence is dense enough that it borders on a catalogue rather than a pointed description.

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 carries the burden of describing return content and does so thoroughly, covering every major tariff component. It omits practical details an agent might want, such as behavior on an unknown label or approximate response size, but nothing essential to invoking 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 100% and the schema already explains the label format (24-char hex), the example, and the optional _apiKey with its DEMO_KEY rate-limit caveat. The description only reinforces provenance ('Labels come from urdb_search_rates'), adding no new syntax or constraint information, so baseline 3 applies.

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 ('Get the FULL structure of one US electricity tariff by its URDB label') and enumerates exactly what is inside: energy-charge tiers, TOU periods, 12x24 schedules, demand charges, minimum monthly charge, voltage category, service type. It also names the sibling that produces the input ('Labels come from urdb_search_rates'), so an agent can separate it from urdb_search_rates without opening either schema.

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 an explicit use case ('This is what you need to actually compute a bill') and identifies the upstream tool that supplies the required label. It does not state when NOT to use it (e.g. bulk retrieval or when only summary attributes are needed, which is urdb_search_rates' job), so it stops just short of full routing guidance.

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