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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so safety is covered. The description adds genuinely new behavioral context: no subscription is executed through the tool and the transaction happens entirely on flytel.fr, which is the single most important thing an agent needs to know here.

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?

Two short sentences with no filler; the restriction (order happens off-conversation) is stated plainly. It is efficiently sized for a one-parameter helper tool.

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?

There is no output schema, so the description correctly carries the burden of describing what is returned (the order URL and prerequisites). It resolves the potential confusion between the mutating-sounding name 'souscrire' and the read-only behavior, leaving little an agent needs beyond it.

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 100% and the single 'forfait' parameter is documented in the schema with an example. The description's mention of the 'forfait présélectionné' corroborates but does not extend the schema, so the baseline of 3 is appropriate.

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 makes clear what the tool yields: the URL of the online order page with the plan preselected, plus a checklist of what to have on hand. This is a specific output, not a tautology, though it is phrased as a description of the content rather than a direct verb+object action, and it does not explicitly differentiate itself from siblings like get_plan or list_plans.

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 closing sentence 'La commande se fait sur le site, jamais dans la conversation' implies the intended use: retrieve the link so the user completes the order externally. However, it never states when to call this tool versus compare_plans or find_best_plan, nor any prerequisite (e.g. a plan must already be chosen). Usage is implied rather than spelled out.

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