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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds real context beyond that: it explains the tool returns step-by-step instructions (iPhone and Android variants), that the brand argument switches to brand-specific steps, and why the check matters for installation success.

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 front-loaded sentences with no filler: purpose, parameter effect, then usage trigger. The final sentence is somewhat long, but every clause carries decision-relevant information for the agent.

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 single-optional-parameter, no-output-schema guidance tool, the description covers what it does, what it returns in human terms, when to call it, and why it matters. Nothing needed to invoke it correctly is missing.

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 baseline is 3, but the description adds the consequence of supplying the optional argument ('brand-specific steps'), which is more than the schema's plain example list conveys. It also clarifies the parameter is optional, matching required=0.

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 action on a specific subject: it explains how a traveller verifies their phone supports eSIM and is unlocked, returning step-by-step guidance. This is clearly distinct from siblings like check_esim_status (which checks an existing eSIM's state) and create_checkout_link.

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?

Explicitly names the when ('before create_checkout_link when the user is unsure their phone will work') and gives the reason ('an incompatible or locked phone is the most common reason an eSIM cannot be installed'). That is both a trigger condition and an alternative-tool reference.

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