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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, but the description adds the traits they cannot express: it is a paid call (0.05 USDC via x402), the caller's own wallet pays, there is a free availability pre-check (GET /v1/signal_delta/availability?since_date=...), and the two-step payment flow (first call without payment_header to receive the challenge, then re-call with the signed header). This is exactly the kind of auth/cost context annotations don't cover.

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-loads cost and the routing condition, and almost every sentence carries information. However, the 'cheap repeat check' idea is restated three times ('the cheap repeat check', 'a cheap stay-current check', 'the intended repeat purchase'), which adds mild redundancy.

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 paid, two-step tool with no output schema, the description covers the return contents, the free availability endpoint, the payment handshake, and cost. Nothing an agent needs to invoke it correctly 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 description coverage is 100%, so since_date and the payment_header flow are already documented in the schema and the description only reiterates them. It adds no syntax or format detail beyond the schema, so the baseline 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?

States a specific outcome — the change list (new, changed, removed Signal headlines) since a baseline date — and explicitly distinguishes itself from signal_latest and signal_history in the same sentence. An agent can route correctly without opening any sibling 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?

Gives explicit when-to-use ('when you already hold an earlier dated brief and only want what changed since that date') and explicit when-not ('Not when you hold no brief yet (use signal_latest) or want the full briefs (signal_history)'), naming the alternatives and the condition that selects each.

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