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

The description discloses behavioral traits beyond the provided annotations: it specifies that it 'reports on the data only and cannot tell you whether any product requires a warning,' and it details the return contents ('counts of total, active and delisted entries...'). This adds context about limitations and scope that readOnlyHint and openWorldHint do not fully capture.

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 three sentences, each earning its place: purpose, usage, and output/limitations. It is front-loaded with the main action and uses no wasted words.

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 zero-parameter metadata tool with an output schema, the description is complete. It covers what the tool does, when to use it, what it returns, and its limitations. The sibling context is also clear from the description's differentiation.

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?

The input schema has 0 parameters, and baseline for 0 params is 4. The description does not need to explain parameters. It focuses on behavior and output, which is sufficient and appropriate.

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: 'Report the size and edition of the embedded Proposition 65 list, and what the listing-mechanism codes mean.' This is a specific verb and resource, and it distinguishes the tool from siblings like check_prop65 or search_prop65 which focus on individual entries.

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 gives explicit use cases: 'Use this to check how current the data is before relying on a lookup, or to interpret the `AB`, `SQE`, `FR` and `LC` codes on an entry.' It also provides a when-not-to-use boundary: 'cannot tell you whether any product requires a warning.' However, it does not explicitly name alternative sibling tools, so it falls short of a 5.

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