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

Annotations already establish readOnlyHint, destructiveHint false, and openWorldHint, so the safety profile is covered. The description adds genuinely useful behavior beyond that: a 1-hour cache that is bypassed when refresh is true, a 90-day ceiling, and the fact that gap days are still returned. It does not describe volume limits or partial-failure behavior across platforms.

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 dense sentences, front-loaded with the core scope (daily trends, max 90, source platforms) before the secondary caching caveat. Every clause carries information the agent needs; nothing is filler.

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 correctly takes on the return-value burden, naming the per-platform metrics and the per-account summary of totals and follower change. There is no output schema or pagination concern, and no required parameters exist, so the remaining gap is minor: it never says what happens when an account has no insights or how multiple accounts are keyed in the response.

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%, so days, refresh, accountId, and workspace are all already documented in the schema, including the default of 30 and the 1-to-90 range. The description restates the max 90 and cache/refresh relationship but adds no syntax, format, or edge-case detail beyond what the schema provides, so the baseline of 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?

The description states a specific verb and resource (daily account-level trends) with a clear scope: last N days, max 90, one row per day. It also enumerates the platforms and metrics returned (Facebook views/engagement/followers, Instagram reach, Threads views), which separates it from post-level siblings. It stops short of naming the adjacent tools (get_account_stats, get_analytics), so the trends-vs-stats distinction must be inferred.

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?

Usage context is implied rather than stated: 'works even for days without new posts' and the cache/refresh note hint at when this is preferable to a live call. There is no explicit when-to-use or when-not-to-use guidance, and no routing to get_account_stats or get_analytics for point-in-time or cross-resource analytics.

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