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

Annotations only supply readOnlyHint=true, so the description carries most of the burden — and it delivers: ordering ('newest first, from the last sync'), the conditional that opens/clicks/views/recipient/subscriber metrics only appear when a Publisher API key is connected, and explicit empty-state behavior. It omits any note on result-size limits or pagination, keeping it below 5.

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 sentences, front-loaded with the returned data and then the filters and the empty-state rule; every clause is informative. The opening sentence is dense with an inventory of metrics but not redundant.

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 job of describing return content (metrics plus ordering and the Publisher-key condition) and the nothing-synced case. It does not mention the default/max limit behavior, which the schema covers, leaving a small gap for a listing 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 coverage is 100%, so the baseline is 3, but the description adds real value beyond the schema: it supplies the `since` date format (YYYY-MM-DD) that the schema omits and restates the enum semantics of `type` in context. `limit` is left entirely to the schema, which is acceptable but not additive.

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 (the user's Substack posts) and enumerates the returned metrics — likes, comments, restacks, word count, opens, clicks, views, recipients, subscriber deltas — so an agent knows exactly what this retrieves. It does not explicitly contrast itself with siblings such as get_substack_post_stats, get_substack_comments, or analyze_recent_posts, so it stops short of a 5.

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?

Filtering behavior is implied (`query` filters titles, `since` drops older posts, `type` narrows) and the empty-result case is handled ('give the user the link it returns rather than guessing'), which is a useful usage rule. However, no alternative tool is named and there is no explicit when-to-use versus when-not-to-use guidance, so usage remains implied rather than directive.

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