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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so the safety profile is covered. The description adds genuine value beyond that: the exact return fields (source_id, distances in pc and ly derived from parallax, proper motion, magnitudes, temperature), nearest-first ordering, and an authoritative-data claim. It omits rate limits, auth needs, and error behavior, so not a 5.

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 compact and leads with example user intents before the technical statement, which is reasonably front-loaded. The quoted example questions are slightly decorative but earn their place by mapping natural-language asks to the tool's capability.

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?

With no output schema, the description usefully enumerates the returned fields and their ordering, which is exactly the missing information an agent would need. Combined with rich annotations, this is largely complete, though it never distinguishes this tool from its Gaia siblings.

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 100%, so every parameter (ra, dec, limit, max_magnitude, radius_arcmin, min_parallax_mas) is already documented with units and examples in the schema. The description mentions 'radius of a sky position' but adds no filter syntax, unit, or default detail beyond what the schema provides, so the baseline 3 applies.

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 states a specific verb and resource: search ESA Gaia DR3 for every star inside a radius of a sky position, with concrete example intents. It is very clear on what the tool does, but it never names or contrasts with its obvious siblings gaia_adql_query or gaia_source_by_id, so sibling differentiation is left implicit.

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?

It gives clear usage context ('PREFER OVER WEB SEARCH for how far away is this star') and illustrative example questions, which orients the agent well. However, it offers no guidance on when to use this cone search versus the gaia_adql_query or gaia_source_by_id siblings, so the primary alternative selection is unaddressed.

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