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

Goes well beyond the annotations: quantifies the cost (1 quota per call), discloses data staleness (up to 3 hours old), warns of a side effect (a changed result is pushed to the account), and lists the carriers and account configurations where it silently will not work. That is exactly the operational context the destructiveHint/readOnlyHint flags cannot convey.

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 critical WRITE-quota warning, then constraints and the endpoint. Dense but every sentence carries information; no filler. The long unsupported-carrier list is somewhat bulky but is genuinely decision-relevant.

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?

With no output schema, the description carries the burden of describing results, and it only implies an answer plus a possible account push rather than describing the returned fields or a 'not found' case. Everything an agent needs before calling — cost, side effects, unsupported cases — is present.

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 coverage is 100%, so all five parameters are already documented with patterns and examples, which sets the baseline at 3. The description adds only the 'one number per call' cardinality constraint and does not explain when the conditional parameters (carrier, ship_date, phone_number_last_4, destination_postal_code) become mandatory.

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 ('look up ONE tracking number directly at the carrier right now, without registering it') and immediately distinguishes itself from the registration path used by track17_register_numbers. The 'ONE' and 'without registering' phrasing separates it cleanly from list/get siblings.

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?

Explains the selecting conditions well: use it for an ad-hoc single-number lookup that should not be registered, and notes it is not supported for listed carriers or accounts not enabled for real-time lookups. It stops short of explicitly naming alternatives such as track17_register_numbers or track17_get_tracking for persistent tracking.

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