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

Annotations already cover readOnly/idempotent/non-destructive/closed-world, so the bar is lower; the description still adds two things annotations cannot express — that the call does not count against check usage, and that it mirrors GET /v1/meta. Missing are any notes on caching or how stale the returned 'last refresh time' can be, which matters for a metadata tool whose whole purpose is freshness reporting.

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?

Four short sentences, front-loaded with the returned payload, then the three qualifiers (not a check, read-only, REST equivalent). Efficient overall, though the enumerated content list plus the 'Same data as GET /v1/meta' sentence partially duplicate each other.

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 an output schema present, the return-value enumeration is not strictly required, and the description nonetheless supplies the two facts an agent actually needs for selection: no check cost and REST-endpoint equivalence. Nothing critical is missing for a zero-parameter metadata lookup, though freshness semantics of the reported refresh time go unstated.

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?

The tool takes zero parameters, so per the rubric the baseline is 4; there is nothing for the description to disambiguate beyond confirming the call is argument-free.

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?

The description opens with a specific verb+resource ('Return the service version and build...') and then enumerates exactly what data comes back (service version, disposable-list version, counts, last refresh, source/licence, limits). This is clearly distinguishable from siblings check_domain and check_email, which return verdicts about a specific input rather than service metadata.

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?

'Does not count as a check' is an explicit routing signal: it tells the agent this call sits outside the check_* quota/accounting path and is safe to call for diagnostics. It stops short of stating when an agent should prefer this over the check tools (e.g. 'use to verify the list is fresh before interpreting a check result'), so it is clear context without explicit usage scenarios.

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