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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), so the description only needs to add context. It does: it flags the API-key requirement upfront and notes that a marginal-fuel flag is published alongside the fuel data, which is a data-shape trait absent from the annotations.

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 sentences, well front-loaded: identity and returned fields first, then usage triggers, then the auth prerequisite. No filler, though the fuel list is long enough to slightly crowd the opening sentence.

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 data tool with no output schema, the description compensates by enumerating the returned fuel categories and the marginal-fuel flag. Pagination defaults are left entirely to the schema, which is a minor gap but not a blocking one.

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% for all three parameters (date, limit, _apiKey), so the schema already carries the semantics. The description adds no parameter-level detail beyond the schema, which is the expected baseline-3 case.

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 ('ISO New England generation by fuel category in MW') and enumerates the fuel categories and the marginal-fuel flag, so the agent knows exactly what data this returns. It does not name the neighbouring ISO siblings (isone_lmp, isone_load), so differentiation is inferred from content rather than stated.

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 three concrete user-intent triggers ('what is New England burning right now', 'ISO-NE renewable share', 'how much gas is New England on') that map cleanly onto the tool. It offers no when-not guidance or explicit alternative (e.g. use isone_lmp for prices), which keeps it below a 5.

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