count_affected_entities

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), so the remaining burden is light. The description adds the useful trait that results are a count rather than a resource list, motivating it for large blast radii, but says nothing about result accuracy, truncation, or cross-account scope.

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 core action and the alternative-routing rule, then a short arg note and example prompts. Nothing is redundant, though the example prompts partly duplicate the usage sentence.

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 an output schema covering the return value and annotations covering safety, the description only needs to convey purpose, scale rationale, and the one input's meaning. It does all three at a basic level; only ARN input specifics are thin.

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 0%, so the description must carry parameter meaning, and it only restates the parameter ('event_arns: One or more event ARNs'). No ARN format, batching limits, or whether mixed event types are allowed are given beyond what the schema name implies.

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 (count affected resources) and immediately distinguishes itself from the listing siblings with 'without listing them'. An agent can tell it apart from get_affected_entities 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 an explicit when-to-use rule: call this before entity-listing tools when an event could touch thousands of resources. It references a category of alternatives rather than naming a specific sibling like get_affected_entities, so routing is slightly less precise than it could be.

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