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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description reinforces that with the explicit 'this call sends nothing', which is the key behavioral reassurance for a preview tool. It also discloses the downstream condition under which the real email is sent, adding context beyond the annotations, though it says nothing about rate limits or whether content is generated on the fly.

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 short sentences, zero filler, with the purpose and returned fields front-loaded and the no-side-effect caveat immediately after. Every sentence earns its place.

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 zero-required-parameter read tool with no output schema, the description covers purpose, return shape, and side-effect behavior, which is nearly everything an agent needs. Only the precondition for a meaningful preview (an existing owner_digest configuration) is left implicit.

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?

With a single optional api_key parameter at 100% schema description coverage, the schema already documents everything needed, and the description adds nothing parameter-specific. Baseline 3 applies since no additional meaning is contributed.

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 ('preview the daily owner digest') and names the returned fields (subject, html, text), so the agent knows exactly what it gets. It does not reference any sibling tool, but the siblings listed (library, reports, rules, keys) are clearly unrelated, so differentiation is not really at stake.

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?

It implies the use case — checking what the daily digest will look like, with the note that the email only goes out if owner_digest is enabled — but it does not state preconditions explicitly (e.g. whether a digest must already be configured) or name alternatives. Adequate but leaves the agent to infer the trigger conditions.

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