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

Annotations already flag non-read-only, non-idempotent, open-world behavior; the description adds real value beyond them by disclosing outcomes per mode (100 credits / 14 days / no human step vs. 2,000 credits monthly / one per email) and an upgrade path. The only gaps are what happens if a trial key already exists or the response shape, but for a small issuance tool this is substantial.

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-loads the key fact ('Free'), then conditions, modes, and the agent instruction. Four tight sentences with no filler; every sentence adds routing or behavioral information.

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 carries the burden of explaining what comes back, and it does by naming the key types, credit amounts, and durations. Minor gaps remain around use_case and the exact response format, but nothing essential for correct invocation 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?

Schema coverage is 75%, so baseline is 3. The description clarifies email and api_key semantics (omit email for starter, pair email+api_key to upgrade), but much of that repeats the schema's own descriptions, and the use_case parameter is left undocumented in both places.

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 the specific action (obtaining a Factline key) and its two variants (instant starter key vs. email-backed trial key). It clearly separates itself from the sibling report/check tools by framing the purpose as key acquisition when free calls run out, not a data lookup.

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 an explicit trigger ('use when free calls for today are used up or the user wants more paid checks without a crypto wallet') and an explicit behavioral instruction ('Ask the user for the email; never invent one'). It also explains the branch condition between the two modes (omit email vs. supply email), so the agent knows which path to take.

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