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

Annotations already cover readOnly/idempotent/non-destructive, and the description adds substantial context beyond them: paid x402 flow, first call without payment_header returns the challenge free, wallet model ('your own wallet pays, never this server's'), free 404 with payment_taken false for unstored dates, and the mutable-revision caveat that it is not an as-of backtesting snapshot. This is exactly the behavioral disclosure a paid, side-effecting-network tool needs.

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 paid price and the core scope distinction, and every paragraph carries decision-relevant content. It is dense and slightly repetitive on pricing ('[PAID — 0.04 USDC...]' plus a second full price sentence plus 'cheaper than buying full history'), which costs a point.

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 exists, so the description carries the return contract and does: what the body looks like ({ date }), what comes back (the date's stored revision), and how to identify it (brief.generated_at, brief_sha256, sha256 previewed free). Nothing an agent needs to call 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 coverage is 100% and both parameters are already well documented, so the baseline is 3; the description adds real meaning by pointing to /health archive_dates and the free editions.json for choosing a valid date, and by clarifying payment_header round-tripping. It stops short of explaining the date format itself, which the schema covers.

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 ('ONE stored date's full Signal brief') and explicitly distinguishes itself from signal_latest and signal_history by the scope each covers. An agent can pick between the three 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?

Explicit when-to-use ('full brief currently stored for one date, e.g. to review judgments and sources') and when-not ('not the most recent edition → signal_latest; not several consecutive days → signal_history'). Alternatives are named with their trade-off (flat price).

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