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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds substantial context beyond them: no execution, zero lookups charged, deterministic rule-based planning with no language model, and the fallback to site_selection with needs_clarification and low confidence. That last piece is behavior an agent could not infer from annotations and materially affects how it should interpret results.

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?

Purpose and the plan-vs-execute distinction are front-loaded, and most sentences carry weight. The middle output-field enumeration reads as a dense run-on and could be tightened, but it is doing real work given there is no output schema.

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 compensates by enumerating the return shape (tool, arguments, estimated_lookups, explanation, matched, needs, ready, confidence) and the degradation behavior. Cost, determinism, and prerequisites are all covered, so an agent has everything needed to call and interpret it.

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% and the schema itself already explains lat/lng pairing, the address alternative, and the mutual-exclusion error. The description adds nothing about any of the four input parameters, so the baseline of 3 is 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?

Uses a specific verb and resource ('Map a plain-English question ... to the tool that answers it') and immediately scopes it as planning-only rather than execution. It explicitly distinguishes itself from the sibling `ask` ('the same planner plus execution'), so an agent can pick between them without reading either schema.

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?

States the when ('Plan only: nothing runs and nothing is charged') and names the alternative with its trade-off ('ask is the same planner plus execution, charged like the tool it calls'). It also gives the fallback path for questions with no recognised topic, leaving no ambiguity about selection.

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