List Contact Topics

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

The readOnlyHint annotation already marks this as a read operation, and the description reinforces that by saying 'List all topic subscriptions.' It adds extra behavioral context by instructing the agent to avoid surfacing IDs unless the user requests them, which isn't captured by annotations.

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 sentences, front-loaded with the primary action. The second sentence is a useful, non-redundant behavioral tip. No wasted words or repetition of schema details.

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 list tool with no output schema, the description covers the core purpose and scope. It doesn't explain pagination beyond what the schema already documents, and doesn't detail ambiguous parameter interactions (e.g., using both id and email), but it provides enough context for typical use. Given the rich schema and annotation, this is adequate.

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 coverage is 100% with each parameter described, so baseline is 3. The description adds meaning by stating the tool operates 'by contact ID or email,' clarifying that one of these identifiers is needed even though the schema marks them optional. This helps the agent decide which parameters to supply.

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 clearly states a specific action ('List all topic subscriptions') on a specific resource ('for a contact in Resend'), and distinguishes itself from sibling tools like list-topics by specifying the contact scope. It also mentions the alternate lookup methods (ID or email), making the purpose unequivocal.

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 implies usage context (for a contact's topics) but does not explicitly compare with alternatives or state when not to use it. The only additional usage hint is about not telling IDs unless asked, which is a response-formatting guideline rather than a tool-selection guideline.

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