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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful context by enumerating the returned fields (numbers, status, pages, duration, type, file URL) and noting the endpoint path. It does not mention pagination behavior, though the schema covers page/next_page.

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?

Two tight sentences plus the endpoint, with the resource and its payload fields front-loaded before the filter note. No filler, though the trailing 'GET /faxes' is marginal value.

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 usefully enumerates what a fax record contains, which is the main thing an agent would otherwise lack. Pagination and limits are fully covered by the schema, so the only gap is explicit routing away from placetel_get_fax.

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%, so every parameter including enums is documented in the schema. The description only restates the two filter dimensions (direction, number) without adding syntax, defaults, or format details, so it sits at the baseline.

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 resource (in- and outbound faxes), enumerates the fields returned, and names the filter dimensions, so it is clearly a listing operation distinct from the singular placetel_get_fax. It lacks an explicit contrast with that sibling, but the plural scope plus filter language makes the distinction inferable.

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?

'Filter by direction or number' implies the usage context (browsing a fax log rather than fetching one record), but there is no explicit when-to-use guidance or stated alternative such as placetel_get_fax for a single fax. Usage must be inferred from the verb and scope.

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