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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, yet the description adds genuinely non-obvious behavior: it costs nothing, the card self-loads the catalogue, the user's pick arrives as a chat message from the user, the card stays live, and a later override message wins completely. That post-call protocol is not derivable from any structured field.

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 action, then WHEN NOT, AFTER, and OUTPUT in a scannable order, and nearly every clause carries operational content. It is nonetheless long for a zero-parameter tool, with heavy capitalization and several overlapping 'do not' prohibitions that could be compressed.

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 no-param, no-output-schema tool, an agent has everything it needs: trigger conditions, exclusions, the exact post-call message to send, what not to do afterwards, and how to handle late overrides. Nothing forces a follow-up call to disambiguate the flow.

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?

Zero parameters, so the baseline is 4; there is nothing to disambiguate. The description does add an OUTPUT note ('one short object naming the catalogue, for the card') plus an instruction not to paste or summarise it, which is useful but not parameter semantics.

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?

A concrete verb plus resource ('PUTS THE SERIES CATALOGUE ON SCREEN as a grid of previews') with what each tile does and what selecting one produces. It explicitly contrasts with `list_series`, so an agent can route between the two without opening either 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?

Gives a positive trigger ('the moment the user wants to make a story episode or asks what story formats exist and has not named one') and a WHEN NOT block with a named alternative and the exact condition (user named a series, asked about one series' details, or the client renders no cards). It even covers the recovery path if the user reports not seeing the picker.

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