search_subscribers

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

Beyond the readOnlyHint annotation, it discloses row limits (1–50, default 10), default return fields, the include parameter behavior, total_matching caveats, pagination not being a snapshot, and that search matching is controlled by Substack. This is rich, non-obvious behavioral detail that helps an agent understand reliability and limitations.

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?

A single paragraph with front-loaded purpose, followed by key constraints and caveats. It is information-dense but not bloated; every sentence contributes meaning. Could be slightly more structured but is appropriately concise.

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?

For a 10-parameter tool with low schema coverage, the description covers critical behavioral aspects (return fields, pagination, search semantics) but leaves several parameters unexplained. An agent might still struggle to construct a correct request without additional parameter insight, though the tool name and schema provide some clues.

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 only 20% (two date params have descriptions). The description mentions 'include selects extra fields' and implies filters/sorting, but it does not explain the meaning or usage of most parameters (sort, limit, offset, search, subscription_types, activity_rating_min/max, etc.). It fails to compensate for the low schema coverage.

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 ('read') and resource ('private subscriber data') with 'Substack-side filters and sorting'. This clearly distinguishes it from public post tools and establishes it as a read operation on subscriber data. Though it doesn't name siblings, the purpose is unmistakable.

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?

Provides context about server-side filtering and sorting, which implies when it should be used, but it does not explicitly state when to prefer this over alternatives like list_subscribers or get_subscriber. No exclusions or alternative routing are given.

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