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), so the bar is lower. The description adds genuinely new behavioral context: the exact return payload fields and the per-request cost ('Billed $0.003 per request'), which the agent cannot see anywhere else.

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?

Front-loaded with the verb and resource, then the return payload, then the identifier constraint and cost. It is dense but every clause carries information; the return-field list is somewhat long, though justified by the absence of an output schema.

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 must describe returns and does so thoroughly (name, tagline, pricing, contributors, etc.), plus it covers identification methods, param exclusivity, and cost. Missing only sibling routing guidance, which is a usage rather than completeness 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 description coverage is 100%, so the schema already documents both parameters and their accepted formats in detail. The description's 'provide exactly one of publication, publication_id' restates the mutual-exclusivity rule already present in the schema, adding no format or edge-case detail beyond it. Baseline 3 is correct.

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 a Substack publication') and enumerates the accepted identifiers (subdomain, custom domain, URL, ID). This clearly separates it from sibling search tools like search_substack_publications — one fetches a known publication, the other discovers them.

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 description tells the agent how to identify the target ('provide exactly one of publication, publication_id'), which implies the usage precondition, but it never names an alternative (e.g. search_substack_publications for finding a publication) or states when not to use this tool. Usage is implied rather than guided.

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