What DFX actually covers, and what it does not

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

Annotations already cover read-only and idempotent, and description adds that it queries no data and is free, plus explains NOT_COVERED is measured not inferred. This goes beyond the 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 verbose with redundant phrases like 'stated plainly' and 'measured rather than inferred', and the structure repeats information about the two modes. It could be half the length without losing meaning.

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 description explains the two output modes (full grid vs direct verdict) and the meaning of NOT_COVERED, providing sufficient context for correct usage. Could benefit from an explicit output structure, but overall it is complete.

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?

Both parameters have clear schema descriptions ('Two letter state code', 'Same vocabulary as search_property_events'), and the tool description explains how they narrow the result. The enum is fully documented.

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 reports coverage ('Measured coverage, served sources, object types and the known gaps') and differentiates from search tools by clarifying it checks a coverage registry. However, the phrasing is ornate and could be more direct.

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?

Explicitly instructs to call before concluding absence ('Call this before concluding that an empty result means an absent market') and provides two calling modes: no args for full grid, with args for direct verdict. This gives unambiguous guidance.

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