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

The annotations already declare readOnlyHint=true, and the description adds genuinely new behavioral context: the operation is free, requires no API key, and returns checkout links supporting crypto or card. This resolves the tension between the name 'buy_credits' and the read-only annotation by clarifying the tool only surfaces packs and links rather than performing a purchase. It does not contradict annotations.

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 short sentences, front-loaded with what the tool returns and followed by the parameter and auth/free details. There is no filler, and every sentence contributes distinct 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?

For a one-optional-parameter, read-only tool with no output schema, the description covers content (packs, prices, checkout links), payment methods, filtering, cost, and auth requirements. The only minor gap is that it does not specify the exact return shape, such as whether checkout links are URLs or embedded fields, but the annotations and schema cover the rest adequately.

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% and the single enum parameter is fully documented in the schema itself. The description adds meaning beyond the schema by explaining the filtering behavior: supplying a pack id returns only that pack, which implies omitting it returns the full set. That is a meaningful behavioral clarification of an optional parameter.

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 names the resource ('credit packs with prices and a direct checkout link') but never states a verb such as 'list' or 'return', leaving the action implied rather than explicit. The tool name 'buy_credits' suggests a transaction, which the description only partially resolves by describing informational output. Siblings are unrelated OSINT tools, so no differentiation is needed, but the verb gap keeps this at a minimum-viable level.

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?

'Pass a pack id for just that pack' implies the optional-filter behavior and suggests omitting it returns all packs, which is useful usage context. However, there is no explicit statement of when to use this versus other tools or any exclusion criteria. 'Free; works without a key too' gives context but not selection guidance.

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