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

Annotations only cover readOnly and openWorld; the description adds substantial behavioral facts beyond them: determinism ('the same coordinate always returns the same identity'), the replayable receipt hash, and the cost model ($0.01 USDC per call after 25 free calls per day). Cost and rate-limit disclosure is exactly the kind of thing an agent needs before repeated invocation and cannot infer from 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?

Front-loaded with the deliverable, then value, then price—a sensible order with no filler sentences. The first sentence is dense with a long parenthetical field list, which costs some readability, but every clause carries information an agent would otherwise have to discover by calling.

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?

There is no output schema, so the description carries the return-value burden and does so by enumerating the card fields, tile bounds and neighbours. Combined with the determinism guarantee, receipt hash and payment terms, an agent has everything needed to decide and call correctly.

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%, so the baseline would be 3, but the description adds genuine meaning: it pins the output granularity to ~19 m at zoom 21 and attributes the eight neighbouring tiles (mapping to includeNeighbours) to the result. It does not restate the latitude range or the _payment payload format, but the schema already covers those.

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?

States a specific verb and resource ('gives any Earth coordinate a stable identity') and immediately enumerates exactly what the identity consists of: a ~19 m world tile at Web Mercator zoom 21, tile bounds/centre, a ROAST-78 card with named attributes, and eight neighbours. This is clearly distinct from siblings like location_context or celestial_earth_projection, which return place or projection data rather than a deterministic per-tile card.

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?

Provides concrete usage contexts ('agents can anchor games, stories, AR scenes and shared worlds to real places') and the pricing/free-allowance condition, which tells an agent when this is economically appropriate to call in a loop. It stops short of naming an alternative tool or stating when NOT to use it, so no exclusion guidance or explicit sibling routing is given.

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