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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the description adds the parts annotations cannot: the entitlement gate, the failure behavior (a payment-required/upgrade object is returned rather than an error), and the payload size (~900 KB). That is substantive beyond structured fields; it falls short of 5 only because it says nothing about whether the response can be streamed or truncated.

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?

Dense and front-loaded: the core deliverable comes first, then entitlement, then fallback behavior, then size. The phrase 'the keyed deliverable of the Corpus/Enterprise license' is mild framing rather than instruction, but the rest earns its place.

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 tells the agent what comes back (one document containing premium bodies), its approximate size, and the alternative success path (an upgrade object). Combined with annotation coverage, nothing needed 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?

The single api_key parameter is fully documented in the schema, so the baseline would be 3. The description goes further by tying the key to specific license tiers and by distinguishing which tier does not grant access, which is semantic meaning the schema's 'Corpus/Enterprise license key (cg_...)' string 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?

States a specific verb and resource ('Return the ENTIRE corpus including premium resource bodies in one document') and immediately scopes it against the sibling get_corpus, which is named as the free premium-stubbed version. An agent can separate the two without opening either schema.

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?

Gives explicit selection conditions: use this when you hold a Corpus-, Corpus-annual- or Enterprise-tier key; otherwise use get_corpus. It also calls out the trap case (a Starter key unlocks premium resources but NOT the corpus file), which is exactly the kind of exclusion an agent needs.

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