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

Annotations already cover read-only/idempotent/non-destructive, but the description adds substantive context the annotations cannot: every received test is public on faxbeep.com for 30 days (with a privacy warning to relay), the email test may be disabled, and server time must be used rather than the agent's own clock.

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?

Front-loads the action and the 'call this first' directive, and nearly every sentence carries operational detail. It is dense and slightly sprawling, with field explanations interleaved with warnings rather than cleanly grouped, but little is wasted.

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-parameter tool with no output schema, the description supplies everything needed: what is returned, how to interpret each field, when data may be missing, and the privacy constraint on the person's test document.

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?

Zero parameters, so the schema baseline is 4. The description goes further and defines the undocumented return fields (local_format vs international_format, email_max_message_bytes semantics with ~1/3 encoding overhead, troubleshooting_url), which matters because no output schema exists.

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 ('Get the Faxbeep test fax numbers, the test email addresses and the limits') and enumerates the payload sections. It also distinguishes itself operationally from list_test_faxes by supplying the 'now' value used as that tool's 'since'.

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?

Explicit ordering instruction: 'Call this first, before the person sends a test.' It also routes the agent onward ('Use it as "since" of list_test_faxes') and explains the condition under which 'email_addresses' is absent (email test off).

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