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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=true), and the description adds genuinely new behavior: a hard 100-profile cap, the exact fields returned, and a per-request cost of $0.003. Cost and pagination ceiling are the kind of operational detail annotations cannot express, though nothing is said about ordering, rate limits, or behavior on an invalid post reference.

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 tightly packed sentences with the core action front-loaded and return contents, input requirement, and billing all earning their place. The parenthetical is dense but not redundant with anything preceding it.

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 compensates by enumerating the returned profile fields and the post's total like count, plus the 100-record cap and the billing rate. It is complete enough for an agent to call the tool confidently, missing only error/failure behavior and any hint that results beyond 100 may be inaccessible.

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 every parameter and its accepted forms are already documented in the schema. The description repeats the identification rule ('url, post_id, or publication together with slug') without adding syntax, format, or precedence detail beyond it, 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?

States a specific verb and resource ('Get the people who liked a Substack post') and immediately enumerates the returned data, which cleanly distinguishes it from siblings like substack_post_details and substack_post_comments without opening any schema.

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?

The parenthetical 'provide url, post_id, or publication together with slug' tells the agent exactly what inputs the tool needs and the valid combinations, which is clear invocation context. It stops short of naming when to prefer this over alternatives (e.g. substack_post_details), so no exclusions are stated.

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