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

Annotations already declare readOnly/idempotent/non-destructive, and the description goes well beyond them: it discloses price (0.05 USDC on Base via x402), that the caller's own wallet pays, that the server never holds a wallet, and the two-step payment-challenge handshake. This is exactly the mutation/payment context an agent 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?

Dense but front-loaded with the payment-gating context before the mechanical details. Every sentence serves a purpose (cost, availability check, no-payment first call), though the payment description is repeated between the prose and the schema-adjacent text.

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, but the description names what comes back (new, changed, removed headlines) and fully covers the payment/auth prerequisite and the availability pre-check. Sufficient for an agent to invoke correctly, though the exact response shape is left implicit.

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%, including the nested payment_header object and its name/value fields, so the schema carries the parameter burden. The description reinforces the payment_header lifecycle but adds little syntax beyond what the schema already documents; baseline 3 applies.

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 (return new/changed/removed headlines) and resource (Signal headlines since since_date), and explicitly distinguishes itself from signal_latest by framing itself as a cheap delta check rather than a fresh re-scrape.

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: intended repeat purchase for an agent holding an earlier dated brief. Gives the exact precondition workflow — call the free availability endpoint first, pay only when has_newer_day is true, and omit payment_header on the first call. Nothing is left to inference.

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