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

Annotations already declare readOnly, idempotent, non-destructive and openWorld, so the safety profile is fully covered. The description's main additional claim, 'without sending a message', reinforces the read-only nature but is largely redundant with readOnlyHint, and it says nothing about what is returned, throttling, or whether the target can observe the lookup.

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 with the core action and its main constraint front-loaded, and no filler. Slightly compressed phrasing ('without sending a message') is the only place a reader has to infer intent.

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?

There is no output schema, so the description is the only place a caller could learn what a profile read yields (fields, whether friends/lists are included), and it is silent on that. Combined with openWorldHint, an agent has no idea of the result shape before calling; safety and input rules are adequately covered.

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 both parameters (account_id and user_id_or_url) are already fully documented, including the 'not a display name or vanity slug' warning. The description restates the accepted input formats rather than adding new syntax or format detail, 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?

Specific verb + resource ('Read a known Facebook profile') with an explicit scope qualifier ('known', numeric ID only). It distinguishes itself from a search/resolve flow by declining vanity-name lookups, though it never names the sibling that does that job (facebook_resolve_person), so the differentiation is by implication rather than explicit routing.

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 a clear usage condition (you already know the person, you have a numeric ID or profile.php?id= URL) and a clear exclusion (vanity names/display names are not resolvable here). It also points to the fallback path ('Resolve a name from friends/contacts and disambiguate') without naming the actual alternative tool, which is the only gap.

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