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

Annotations already declare readOnlyHint and idempotentHint, so safety is covered. The description adds genuinely non-obvious behavior: followers are a 'stand' (latest value plus change) and are 'never added up across channels', which prevents a real aggregation error an agent would otherwise make. It also discloses that posting capability per channel is included.

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 sentences, front-loaded with the resource and scope, then the returned fields and one consumer hint. The parenthetical about follower stands is dense but load-bearing; 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 carries the burden of describing returns and does so by listing metrics, channel ids, and posting capability. Only minor gaps remain (result ordering or granularity per channel/period), which are not critical for a read-only aggregate tool.

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%, and the schema already documents site_id provenance (from list_sites) plus the from/to date formats and defaults. The description only restates 'over a period' without adding format or default detail, 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?

States a specific verb+resource (social figures per channel of a website over a period) and enumerates the returned metrics: followers, reach, engagement, views, posts. An agent knows exactly what data this returns, though it does not explicitly contrast itself with nearby siblings like get_site_metrics or get_ads.

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 is implied by the scope statement, and the closing clause gives one concrete downstream use (channel ids are 'needed for propose_post'). There is no explicit when-not guidance or named alternative for overlapping metric tools, leaving selection partly to inference.

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