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

With readOnlyHint, openWorldHint and destructiveHint already covering the safety profile, the description adds genuinely new operational context: the $0.003 per-request billing and the result field set. It does not restate annotation content or contradict it. Rate limits and pagination depth are left to the schema, which keeps this short of a 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?

Two sentences, zero redundancy: capability and scope first, then return payload and cost. Nothing is padded and the most decision-relevant information is front-loaded.

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 read-only list tool with no output schema, the description supplies the return field list, the sort/search modes, and pricing — enough to call it correctly. The only minor gap is the absence of guidance on result volume or how the paid sentiment surcharge interacts with paging, though the schema's get_sentiment text partially covers the latter.

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 (page size, query limit, sort enum, publication identifier formats) is already documented in the schema. The description's mention of sort modes maps onto existing enum values and adds no syntax, defaults, or format detail beyond it. Baseline 3 applies when the schema carries the burden.

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?

Names a specific verb+resource (get a publication's posts) and immediately bounds the variants: newest first, top, discussions, or keyword search. Also enumerates the returned fields, which lets an agent distinguish it from siblings like substack_publication_details or substack_post_details without opening a 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?

Usage is only implied through the sort/search enumeration ('top or most discussed, or search them by keyword'). There is no explicit guidance on when to choose this over search_substack, substack_user_posts, or substack_category_feed, nor any stated prerequisites. Adequate but leaves routing to inference.

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