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

While annotations already declare readOnlyHint=true and destructiveHint=false, the description adds valuable context beyond them: a required API key (auth need), the returned fields (subject, status, send time), and crucially the empty-list-not-an-error semantic that prevents agents from misinterpreting an empty result as a failure. No contradictions with the safe-read annotations; in fact, the description's safety framing aligns with them.

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?

Four sentences, each carrying a distinct, useful purpose: what the tool does, when to use it, what it does NOT do plus auth, and how to interpret empty results. The core purpose is front-loaded in the opening sentence. There is zero redundancy, and 'Requires an API key' plus empty-list semantics earn their place in the description.

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 low-complexity tool with 1 optional parameter, full schema coverage, complete annotations (readOnly, idempotent, openWorld, non-destructive), and no output schema, the description covers all essential aspects: purpose, usage scenarios, side-effect guarantee, auth requirement, returned fields, and error semantics. An agent has everything needed to invoke this 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% — the schema fully documents the single 'limit' parameter (integer, 1-50, default 10). Per rubric, this establishes the baseline of 3. The description's 'newest first' adds ordering nuance, but the schema description already includes that same phrase ('newest first'), so the description adds marginal value beyond the schema for this dimension.

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 first sentence uses a specific verb-resource-scope structure ('List newsletter issues the account has sent or scheduled, newest first'), immediately clarifying what is listed and the ordering. The focus on 'issues' (sent/scheduled content) inherently distinguishes it from sibling list tools like list_newsletter_subscribers, which the description also names explicitly.

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 provides explicit when-to-use scenarios: 'check what went out and when' and 'confirm a scheduled send exists before queueing another.' It also names the precise alternative for a different need ('For WHO receives them, use list_newsletter_subscribers'), giving explicit exclusion criteria that prevents mis-selection.

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