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

Annotations already indicate readOnlyHint, idempotentHint, and non-destructive. The description adds that data is 'real-time for today' and 'timestamped MW values per fuel type', providing useful behavioral context without contradicting 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: first states purpose and content, second specifies return format, third gives example use cases. No unnecessary words, well-structured and front-loaded.

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?

Given simple tool with one optional parameter and comprehensive annotations, the description covers data source, time frame, fuel types, granularity, return format, and example queries. Complete for agent to understand invocation.

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% with a single optional parameter 'limit' whose description explains default and granularity. Description mentions '5-minute interval' which reinforces schema but adds no new parameter semantics beyond what schema provides.

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?

Description clearly states the tool returns CAISO real-time grid fuel mix, listing specific fuel types (solar, wind, etc.) and granularity (5-minute intervals). It explicitly distinguishes from sibling tools like ercot_fuel_mix by specifying 'California' and 'CAISO'.

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?

Description provides specific use cases: 'what is California using to make electricity right now', 'solar curtailment today', 'battery contribution this evening.' It indirectly differentiates from siblings like caiso_demand or caiso_co2 by focusing on fuel mix. Could be more explicit about when not to use, but sufficient.

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