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

Annotations already declare readOnly/idempotent/openWorld, so the safety profile is covered. The description adds genuine context beyond them: the data is sourced from the USGS/EPA Water Quality Portal code service and represents authoritative controlled vocabulary, which tells the agent results are canonical codes rather than user data. No return-format or rate-limit disclosure.

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?

Three tight sentences: purpose, the call-order guidance front-loaded, then provenance. Zero filler, and the most actionable instruction ('Call this FIRST') appears early.

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?

A zero-required-parameter lookup with full schema coverage and read-only annotations; no output schema exists, so the description only needs to convey what it returns, which it does at the level of 'exact controlled-vocabulary spelling.' Slightly more on the return shape (code list vs. single match) would complete 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%, so baseline is 3. The description pushes above baseline by illustrating the case-sensitivity semantics of the domain parameter ('nitrate' is not valid, 'Nitrate' is), which is behavior the schema does not convey.

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?

Specific verb (look up) plus resource (controlled-vocabulary spelling) with the exact scope enumerated: analyte, site type, organization, state/county code. It is clearly distinguishable from siblings like wqp_search_sites and wqp_get_results, which consume these codes rather than resolve them.

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?

Explicitly states when to use it: 'Call this FIRST when a name might not match,' with a concrete failing example. It stops short of naming the downstream alternatives (wqp_search_sites, wqp_get_results) or stating when-not-to-use, so it is clear but not fully routing.

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