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

Annotations already declare a safe, idempotent, non-destructive read. The description adds the auth requirement ('Requires a PJM API key') and the data-freshness semantic ('per published interval'), which the annotations do not cover. It does not discuss rate limits or empty-result behavior, so not 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?

Two sentences, zero filler, with the core content and scope front-loaded before the usage hints and the API-key note. Nothing is repeated from the structured fields.

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 compensates by naming the returned measures and granularity. Combined with the auth note and the interval semantics, an agent has enough to call this correctly without opening the schema.

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 enumerates fuel types (coal, natural gas, nuclear, wind, solar, hydro, oil, storage, other) that expand on the schema's shorter examples for fuel_type. It still says nothing about row_count or default range behavior beyond the schema.

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 ('PJM generation by fuel type') and enumerates the returned measures (MW generated and percentage of total) and the fuel categories. It is clearly distinguishable from siblings like pjm_lmp_realtime (prices) and pjm_load_forecast (demand).

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?

Provides concrete trigger queries ('what is PJM burning right now', 'PJM nuclear share', 'PJM coal vs gas') that map user intent to this tool. However, it never names an alternative tool or states when NOT to use it, so routing among the pjm_* siblings is left partly to inference.

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