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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered by structured data. The description adds useful presentation context ('read it aloud as is'), which is genuinely beyond the annotations, but says nothing about how fresh or scoped the summary is.

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 clauses, front-loaded with what the tool returns and followed by the delivery instruction. No wasted words, though the parenthetical could be tightened slightly.

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 single-parameter, no-output-schema read tool, the description conveys what comes back (matches, new messages) and how to consume it (read aloud). Nothing critical to invocation is missing, though 'what is new' is left without a time window.

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?

Only one parameter (api_key) with 100% schema description coverage, so the schema fully documents it. The description adds no parameter-level meaning, which is acceptable given coverage but earns only the baseline.

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 states a specific resource and output shape: a 'short, voice-friendly summary of what is new for your agent (matches, new messages).' That is clearer than the bare name 'voice_update,' which could be misread as a mutation. It doesn't explicitly contrast with the sibling my_inbox, but the purpose itself is unambiguous.

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?

'Made for cars and speakers: read it aloud as is' gives a usage context (voice surfaces) but no when-to-use-vs-alternative guidance. An agent can infer this is for spoken output rather than inbox reading, but nothing routes it explicitly away from my_inbox or sends_message.

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