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

Annotations (readOnlyHint, openWorldHint, idempotentHint, destructiveHint) already convey safety and idempotency. The description adds value by specifying 5-minute interval data and the most recent published day. No contradictions.

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?

The description is only two sentences, front-loading the core purpose and then usage. Every word is necessary; no wasted text.

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 simple tool with one optional parameter and no output schema, the description covers purpose, data content, and usage. It could mention return format more explicitly, but the mention of 'MW per 5-min interval' suffices.

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?

With 100% schema description coverage, the description adds the default value ('defaults to yesterday') and format hint, going beyond the schema's definition. This is helpful for an agent.

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 clearly states the tool provides NYISO real-time grid fuel mix for the most recent published day, listing all fuel types and units (MW per 5-min interval). It distinguishes from sibling ISO fuel mix tools (caiso_fuel_mix, ercot_fuel_mix) by specifying 'New York' and from nyiso load tools by focusing on fuel mix.

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?

The description explicitly says 'Use for New York grid mix yesterday, NYC clean-energy progress tracking,' providing clear usage context. It does not explicitly state when not to use or list alternatives, but the context is sufficient given the sibling tool names.

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