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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable context beyond that: it discloses that a link is returned, payment happens externally on haalaan.com, and 'Nothing is charged here'—reinforcing and clarifying the financial behavior for the agent.

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 short sentences, front-loaded with the trigger condition, then the outcome and the key reassurance. No filler or repetition; every sentence earns its place.

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?

The tool is simple (one param, output schema exists, safety covered by annotations). The description gives enough to understand when to invoke and what to expect, though it leaves the 'slug' parameter unexplained—a minor gap given the schema pattern.

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 description coverage is 0% for the single required parameter 'slug'. The description implies a plan is selected but never explains what 'slug' represents or how it maps to a plan. With low coverage, the description should compensate but does not.

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 states a specific outcome: returning a haalaan.com link where the traveller pays, and explicitly clarifies no charge occurs here. It distinguishes from sibling tools (readiness, destinations, eSIMs) by focusing on checkout, though it does not literally name 'checkout link' in the description.

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 opening sentence gives a clear triggering condition: 'Use this when the traveller picks a plan.' It does not name alternatives or when-not-to-use cases, but none of the siblings overlap, so the context is sufficient.

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