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

Annotations already disclose destructive=true, non-idempotent, open-world behavior, and the description adds genuinely useful context beyond them: 'charges credits' (financial side effect) and 'enabled endpoint' (access prerequisite). No contradiction with annotations; the description complements rather than duplicates them.

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?

Nine words across two clauses, with the action ('Call an enabled endpoint') front-loaded and the cost warning attached. Every word earns its place; nothing is redundant or extraneous.

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 output schema and rich annotations cover returns and safety, and the schema documents the approval_token/idempotency_key linkage to estimate_cost. However, the minimal description leaves the full execution workflow (estimate → approve → execute → retrieve) implicit, which is a notable gap for the central invocation tool in this ecosystem.

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%, with all six parameters documented in the input schema, so the baseline of 3 applies. The description itself adds no parameter-level meaning, but it does not need to since the schema fully covers param semantics.

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 verb and resource ('Call an enabled endpoint') plus provenance ('found via search_apis') and a distinguishing behavior ('charges credits'). This cleanly separates it from siblings like search_apis (discovery), describe_api (description), and estimate_cost (pricing), so an agent can route correctly without opening schemas.

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 phrase 'found via search_apis' implies the correct workflow (discover first, then execute) and 'charges credits' hints that cost approval may be needed, but the description never explicitly names alternatives or exclusion conditions. It does not tell the agent when to prefer estimate_cost for pre-flight or get_call_result for retrieving async results, leaving routing to inference.

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