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

Annotations already declare readOnlyHint and openWorldHint, and the description adds real value on top: newest-first ordering, the returned metric fields, the caveat that Substack exposes no view counts, and a 1-credit cost. That's solid beyond-schema context, though nothing is said about failure modes for invalid publications.

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?

Four short, front-loaded sentences that each carry information: purpose, payload, data caveat, pagination, cost. Minor waste in the leading fragment 'Publication posts,' which restates the title, but nothing else is padded.

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 4-parameter read tool with no output schema, the description covers return contents, ordering, pagination, and cost, which is most of what an agent needs. The unexplained `limit` and `cache_max_age` parameters are the remaining gap.

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 50%: publication and cursor are documented in the schema, and the description only restates cursor paging. The `limit` (default 20) and `cache_max_age` parameters get no explanation anywhere, so the description doesn't compensate for the coverage gap.

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 resource and scope: a publication's posts, newest first, including the fields returned (reactions, comments, restacks, word count). It's clear it lists many posts rather than one, but it never names substack_post or substack_comments, so differentiation from siblings is left to the agent.

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 'Publication posts' framing plus the cursor instruction implies usage, but there is no explicit when-to-use, when-not-to-use, or pointer to the single-post or comments siblings. An agent must infer the boundary itself.

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