newsletters

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

Annotations already declare readOnlyHint=true and openWorldHint=true, but the description adds genuinely non-derivable behavior: it explicitly will not unsubscribe, and results arrive wrapped in an UNTRUSTED block that the agent must treat as data only. That prompt-injection warning is high-value context for a tool pulling third-party email content. It doesn't mention cost or scan time despite a max of 2000 emails, which is the main remaining gap.

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?

Three sentences, front-loaded with the core function, then the no-side-effect guarantee, then the security caveat — each sentence does work. Slightly redundant phrasing in 'It only reports: it never unsubscribes on its own,' but nothing extraneous.

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, the description carries the burden of describing returns and does so adequately: volume-ranked rows with declared unsubscribe links, wrapped in an UNTRUSTED envelope. Row limits and defaults are covered by the schema, so the definition is complete enough to invoke 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?

Schema description coverage is 100%, so all four parameters (max, top, query, account) are already documented in the schema. The description's reference to 'a period' loosely maps to the query default (newer_than:90d) but adds no syntax, default, or interaction detail beyond the schema; baseline 3 applies.

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 gives a specific verb and resource ('Lists the mailing lists and newsletters'), plus the scope ('that wrote in a period') and the payload of interest ('by volume, with the unsubscribe link each one declares'). This is clearly distinguishable from write tools in the sibling set, but it never contrasts itself with the closest read sibling, sender_stats, which likely overlaps in what it aggregates.

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 rather than stated: the mention of a period and unsubscribe links suggests the agent should call it to survey and locate opt-out links. There is no explicit when-to-use/when-not guidance and no named alternative such as sender_stats or search_emails for related questions.

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