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

Goes well beyond the readOnly/idempotent annotations by disclosing pricing ($0.40), the free-teaser fallback shape (coverage + confidence + would_cost_usd), and the billing-safety behavior for out-of-coverage addresses (coverage:false, never billed). This is exactly the auth/cost/edge-case context annotations cannot carry.

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-loads what is measured and why it matters, then layers on outputs, pricing, and coverage behavior. Dense but every clause carries information; only the long em-dash-heavy opening sentence is slightly overloaded.

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 still lists the return payload (velocity in mm/yr + in/yr with uncertainty, seasonal amplitude, total motion, plain-language assessment, confidence, provenance), covers the paid/free distinction, and handles the out-of-coverage case. Nothing an agent needs to call it correctly is missing.

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 all six parameters are already documented in the schema. The description reinforces the _apiKey-paid vs no-key-free semantics but adds no syntax or format detail beyond what the schema states; baseline 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?

States a specific measurement (Sentinel-1 InSAR vertical land motion in mm/yr and in/yr) for a specific resource (US address), and explicitly scopes it against the nearest siblings by naming only subsidence/uplift rather than general ground data. An agent can distinguish this from sibfly_coverage and sibfly_timeseries on purpose alone.

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?

Enumerates concrete use cases (foundation risk, subsidence, sinkhole/settlement concern, real-estate due diligence, 'is this address sinking?') and gives a clear conditional: with _apiKey it is paid, without it returns a free teaser. It does not explicitly route between sibling tools (e.g., when to use sibfly_coverage or sibfly_timeseries instead), so it stops 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.