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

readOnlyHint=true already establishes the read-only nature, and the description adds meaningful behavior: data is fetched live from Substack at call time and then stored on the post, which is useful context. There is no contradiction with the annotation.

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 concise, front-loaded sentences: the first names the operation and key metrics, and immediately flows into the only parameter detail the agent needs. No redundant filler or restatement of the title.

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?

The tool has one required parameter, a read-only annotation, and no output schema, so the description carries reasonable weight. It enumerates the returned metrics, explains the slug format, and names a sibling that lists slugs. It is slightly thin on response shape, but adequate for a simple read call.

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?

The schema only says the parameter is 'The post slug, from its URL.' The description enriches that by defining url_slug as the part of the URL after /p/ and points to get_substack_posts as the source for valid values. This is a meaningful addition, even though schema coverage is already 100%.

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?

The description names a precise operation: retrieving fresh stats for a single Substack post, and enumerates the metrics returned, distinguishing it from siblings like get_substack_posts or subscriber-count tools. It clarifies the resource scope ('one Substack post') and points to get_substack_posts for slug discovery.

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 clearly signals when to use this tool: when you need per-post metrics like opens, clicks, clicks, views, and revenue. It also explains how to obtain the required url_slug via get_substack_posts. It does not explicitly contrast with the subscriber-focused siblings, leaving some selection reasoning to the agent.

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