purchase_esim

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

With no annotations, the description must carry the transparency burden. It discloses the price-locking behavior ('fetches the live price and ties max_price_cents to it'), which is valuable, but it omits other key traits like reversibility, failure handling, or what the response contains. The unexplained mention of 'max_price_cents' (not in schema) is confusing and could mislead, preventing a higher score.

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 concise sentences: the first states the core action, the second explains the quote-then-commit mechanism. No redundant words or filler; every phrase 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?

For a single-parameter tool with no annotations or output schema, the description covers the essential purchase flow and price guarantee. However, it lacks clarity on what happens after purchase (e.g., order confirmation, eSIM delivery), which is significant for a transactional tool, but given the simplicity, it is mostly complete.

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?

The schema fully documents plan_id with 'prod_xxx from search_esim_plans', so baseline is 3. The description adds no extra parameter-level detail; its mention of max_price_cents is about an internal price cap, not an input parameter, and could even cause confusion about the parameter list.

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 clearly states 'Purchase an eSIM plan' with a specific verb and resource, distinguishing it from siblings like search_esim_plans, get_esim_status, and topup_esim. The term 'Purchase' is unambiguous and directly contrasts with search/topup operations.

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 'Quote-then-commit' phrase provides clear procedural context: the agent should first see a live price before committing. However, it does not explicitly name alternatives or exclusions such as when to prefer topup_esim or re-purchase scenarios, so it falls short of full 5.

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