faxdrop_pair_number

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

Annotations (destructiveHint=false, idempotentHint=true, openWorldHint=true) are consistent. The description adds valuable behavioral context: it writes to a persistent file, requires user confirmation, and notes that validation still applies. No contradictions.

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?

The description is structured with clear sections (USE WHEN, DO NOT USE, SIDE EFFECTS, VALIDATION, RETURNS). Every sentence adds value, and the total length is appropriate for the complexity.

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?

Despite no output schema, the description explicitly states the return format ({ paired, country, type }). It covers side effects, persistence, user confirmation, and validation. Annotations and one parameter make this a well-rounded description.

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?

The input schema has 100% coverage for the single parameter (recipientNumber), describing E.164 format. The description adds meaning by explaining that validation checks (type, country) still apply at pairing time, which goes beyond the schema.

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 clearly states the tool's function: 'Add a fax number to the per-recipient whitelist (paired.json).' It distinguishes itself from siblings (faxdrop_get_fax_status and faxdrop_send_fax) by specifying that it is for pre-approving recurring recipients to skip confirmation in faxdrop_send_fax.

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 explicitly gives when to use ('server runs with FAXDROP_MCP_NUMBER_GATE=pairing and the user wants to pre-approve a recurring recipient'), when not to use ('gate mode is open or closed'), and an alternative ('For one-off faxes, skip pairing and call faxdrop_send_fax directly').

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