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

Annotations only establish that this is an open-world, non-idempotent, non-destructive write. The description adds substantial operational context the agent cannot get elsewhere: per-day key and validation quotas, request and revocation byte limits, and series/matrix cardinality caps. This is exactly the kind of rate-limit and quota disclosure that earns full credit.

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 purpose and the 'rarely needed' caveat before the quota list, so the most decision-relevant information comes first. The quota sentence is long and includes limits for adjacent endpoints (key revocation, series, matrices) that are not this tool's concern, which is mild scope creep.

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?

An output schema exists, so return-value detail is not required, and the description fully covers prerequisites, when to skip the call, and quotas. It never says whether calling it twice produces the same or additional keys, though idempotentHint=false partially covers that.

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% and there is a single optional 'label' parameter already documented in the schema. The description adds no meaning beyond it (no naming conventions, uniqueness, or default behavior), so the baseline 3 applies.

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 and resource ('Issue a free validation key for this session'), which immediately distinguishes it from the validate_* siblings that consume such keys. The word 'free' and 'for this session' scopes the artifact being produced.

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 says the tool is 'rarely needed' and names the conditions under which it is unnecessary: the first validation self-issues a key unless CANLI_KEY or local mode is set, and read tools need none. That is genuine when-not-to-use guidance, not just a when.

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