start_agents_purchase

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

With no annotations, the description carries the full behavioral burden and mostly does: it discloses that the call itself charges nothing and only returns a Stripe checkout_url, documents the 409 product_coming_soon failure for 'architect', and states the duplicate-subscription refusal. It omits auth/permission requirements and rate-limit behavior, which is the only meaningful gap for a mutating purchase-start tool.

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?

Front-loaded with the action and the reassuring 'THIS CALL CHARGES NOTHING' caveat, then organized into pricing, architect, and constraint blocks. Slightly long with some repetition (the architect rule is stated twice in effect), but every paragraph 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?

No output schema and no annotations, yet the description describes the return payload (monthly fee breakdown plus checkout_url), the pricing model, the error conditions, and the preconditions for calling. Nothing essential for correct invocation 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 0%, so the description must compensate, and it does: site_name is explained as the billing/scoping key, agents is framed as the per-agent selection driving price, and the 'architect' exclusion plus the $100/mo-per-agent and $750/mo-bundle pricing semantics are added. It does not restate the enum values or the minItems=1 constraint, but the schema covers those.

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 ('Start a NEW UNS Agents subscription for a named site') and immediately distinguishes itself from siblings start_purchase (all-agents bundle), add_agents, and remove_agents. An agent can tell exactly which of the store/purchase family to call without opening a schema.

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 scopes usage: 'Only for a site that has no subscription yet', warns that a duplicate site_name is refused, and names the correct alternatives (add_agents / remove_agents) for modifying an existing subscription. It also prescribes a human confirmation step before calling.

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