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

Annotations already declare readOnly, idempotent, non-destructive and open-world behavior, so the description only needs to add context. It does: the access is entitlement-gated on payment, and the accepted session_id may come from a single decision purchase or from a bundle (full brief, team license, pack, all-access). The only gap is the failure mode for unpaid or expired sessions.

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 sentences with zero filler; the paid-access constraint is front-loaded before the parameter guidance. Every clause carries information the agent needs to select and call the 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?

For a read-only, two-parameter tool with no output schema, the description covers the access model and both input sources adequately. A brief note on what 'evidence' contains or what an unpaid call returns would close the remaining gap.

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 50%, and the description meaningfully extends the session_id parameter beyond the schema's 'Stripe Checkout Session id' by explaining its two provenance paths. decision_id remains undocumented in both places, though 'one decision' / 'this decision' makes its role inferable.

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 gives a specific verb and resource ('Returns the full evidence for one decision') plus the gating condition ('once it is paid for'), which distinguishes it from the brief-oriented sibling. It stops short of explicitly contrasting itself with get_decision_brief, so the distinction between 'evidence' and 'brief' is left implicit.

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?

It states the key precondition (the decision must be paid for) and tells the agent where to obtain the session_id, naming buy_decision_evidence and the qualifying purchase types. It does not say what to do when the prerequisite is unmet (error vs. empty result) or point to a fallback tool such as get_decision_brief.

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