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

Annotations already declare readOnlyHint=true and the description's 'Read' is consistent with that. The description adds that limits/quota data is surfaced, but says nothing about whether the result is per-key or per-site, how quota windows or resets work, or what happens when the site_url is unknown to the OTP API.

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?

One short sentence, front-loaded with the verb and resource, with no filler. The trailing 'usage or limits' is slightly loose phrasing but still earns its place by indicating the returned data type.

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 one-parameter read tool with annotations covering safety, the description is close to sufficient, but with no output schema the burden of describing return values falls on the description, and 'available usage or limits' is too vague to tell an agent what fields or units to expect.

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% and the single parameter site_url is already well documented in the schema, including its purpose and format. The description adds no parameter-level information, so the 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?

States a specific verb and resource ('Read OTP usage for the API key') plus the scope of what is returned (available usage or limits), which clearly separates it from the send_otp/verify_otp siblings. It does not explicitly name those siblings, but the read-only framing makes the distinction obvious.

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?

There is no explicit 'use this when...' statement or exclusion. The phrase 'including available usage or limits' implies a pre-send quota check, but the agent must infer that this is the tool to call before send_otp rather than being told.

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