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

Annotations already cover readOnlyHint, destructiveHint, and idempotentHint. The description adds behavioral traits beyond those: it returns the whole published set (not a sample), orders by size (largest first), and includes specific fields (charges, S&P 500 overlap). This adds useful context that the agent needs to know. No contradiction with 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?

The description is two sentences with no fluff. The core functionality is front-loaded, and the usage guidance is concise. Every word earns its place, and it avoids unnecessary repetition of schema or annotations.

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?

The tool has no output schema, so the description should explain the return values. It mentions the fields (charges, S&P 500 overlap) and ordering, which is good. However, it does not explain the 'limit' parameter or any pagination behavior, and it does not mention any prerequisites or edge cases. For a simple list tool, this is adequate but leaves the limit parameter unexplained.

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 0%, so the description must compensate. It implicitly clarifies the 'theme' parameter by referencing 'Every US listed fund in a theme,' but it never explains the 'limit' parameter. The phrase 'returns the whole published set rather than a sample' even suggests that limit might not be used to restrict results, which could confuse the agent about its purpose. The description fails to add meaning for one of two parameters.

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's function: 'Every US listed fund in a theme, largest first, with what each charges and how much of it is already in the S&P 500.' It uses a specific verb ('returns' implied) and resource ('funds in a theme'), and distinguishes itself from siblings by noting it returns the whole published set rather than a sample.

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 THIS for any "what X ETFs are there" or "top X ETFs" question,' giving clear when-to-use guidance. It also implies that other tools may return samples, but it does not name specific alternatives like etf_search or etf_rankings. This is strong guidance but could be more explicit about when not to use it.

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