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

Annotations already cover readOnly, idempotent, non-destructive behavior. The description adds useful beyond-annotation context: reading the counts marks nothing as read, which prevents an agent from assuming a side effect. It does not discuss rate limits or refresh behavior, but for a simple read tool with annotations this is adequate.

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?

The description is front-loaded and compact. It repeats the three badge categories in the first and second sentences, which is slightly redundant, but the second sentence earns its place by expanding activity into likes, replies, new followers, and restacks.

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 and no parameters, the description carries the burden of explaining what is returned. It does so by enumerating the three badge types and clarifying that reading is non-mutating, leaving no material gap for calling this tool correctly.

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?

There are zero parameters, so the baseline is 4. The description does not need to explain parameter syntax, and the empty schema is consistent with the tool's purpose.

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 states a specific retrieval: unread direct messages, message requests, and activity notification counts. It names the exact resource categories and frames the tool as returning the Substack app badges, so an agent can tell this apart from list_activity or list_conversations 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?

Usage is implied by the badge/notification framing, but the description does not explicitly say when to use this tool versus alternatives such as list_activity or get_daily_stats. It also gives no prerequisites or exclusions, leaving the agent to infer context.

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