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

No annotations exist, so the description carries the full burden, and it does reasonably well: 'Lists' implies a read-only operation, 'on a date' signals point-in-time, as-of-date semantics, and 'Free' discloses cost behavior. It stops short of describing response structure or any rate/limit behavior, which for a bounded 50-state list is minor.

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 core verb+resource, and the extra clauses (no-tax states, 'Free') are informative rather than padding. The first sentence is a long run-on enumeration, which slightly hurts scannability.

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 and no annotations, the description compensates by enumerating the returned fields (thresholds, logic, measurement period, marketplace rules, registration timing, official source) and the no-statewide-tax states. That is essentially complete for a reference-list tool, though it never states the shape of the response.

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 already 100%, so the baseline is 3. The phrase '(or one state) on a date' reinforces the state and date parameters and hints at as-of-date threshold semantics, but adds little beyond what the schema properties already say.

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 ('Lists') and resource ('economic nexus threshold of every US sales tax state'), with rich detail on what the listing contains. It does not, however, draw an explicit contrast with the sibling check_economic_nexus, so an agent must infer that this is a reference lookup rather than a per-business check.

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?

Usage is implied by the content (reference lookup of state thresholds), and the optional state narrowing is noted, but there is no explicit when-to-use guidance, no when-not-to-use, and no reference to the alternatives check_economic_nexus or list_upcoming_nexus_changes.

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