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

Beyond the readOnly/openWorld annotations, it discloses that validation and check-digit computation happen locally, that the owner data comes from a named public register (prefixlist.com), and gives precise pricing mechanics ($0.002 USDC per successful call via x402 on Base/Solana/Arc, with failed calls uncharged). That is exactly the kind of cost and side-effect context annotations cannot express.

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?

Three sentences, verb first, then capability scope, then the negative scope, then cost. No filler and no repetition of the title; every clause carries information an agent needs.

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?

An output schema exists, so return values need no prose, yet the description still summarizes them at a useful level. With a single 100%-covered parameter, explicit cost terms, and a stated data provenance, an agent has everything needed to decide and invoke correctly.

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% and the schema already gives the format and an example, so the baseline is 3. The description adds meaning by decomposing the identifier into owner code, category, serial, and check digit, telling the agent what the input is actually validated against rather than just its shape.

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 ('validates an ISO 6346 container number'), then enumerates exactly what is returned: owner name, country, website from prefixlist.com, and tracking links. It also explicitly distances itself from live milestone lookup, which separates it from tracking-oriented siblings like logistics_vessel_tracker.

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?

'It does not read the container's live milestones (carriers publish them on their own sites)' tells the agent a clear when-not condition, which is strong guidance for a tool that superficially resembles a tracker. However, it does not name a specific sibling tool to use instead, so the routing is implicit rather than explicit.

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