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

Annotations already cover the safety profile (readOnly=true, destructive=false, openWorld=true), and the description adds substantial behavior beyond them: exact per-call price and chains, the x402 payment handshake, that an unpaid call returns isError with a fresh invoiceId rather than failing silently, and that unpaid calls cost nothing. None of this contradicts the annotations, and the return-field list compensates for the absent output schema.

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?

The pricing and pay-per-call framing is front-loaded, then the single question the tool answers, then the return fields, then the error/retry path. Nearly every sentence carries information, though the price is stated twice (title and first sentence) and 'Unpaid calls cost nothing' is partly redundant with the preceding error-handling sentence.

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 two-parameter read tool with no output schema, the definition covers cost, payment mechanics, failure mode, retry path, and returned fields — enough for an agent to invoke it correctly. Remaining gaps are minor: no pagination or rate-limit guidance, no indication of how large the 'tracked domains' set is, and no note on whether a paid call is idempotent or repeatable across invoiceIds.

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 both parameters (since, payment_signature) are already fully documented, including the 7-day default. The description only echoes 'since a time' and points at payment_signature as an alternative channel for the signed payload; it adds no format or boundary detail beyond what the schema states. 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?

The description states a specific verb and resource: 'Which tracked domains changed their public agent-access files since a time,' with 'Raw domain, path, times, hashes, HTTP status, and robots.txt group deltas' clarifying the payload. It implicitly contrasts with the single-domain sibling get_access_policy_reading by scoping to 'all tracked domains,' but never names that sibling, so the differentiation is left to inference rather than made explicit.

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?

Usage is clear: call this to find which tracked domains changed since a time, and the payment flow is spelled out step-by-step (first call without payment yields PaymentRequired + invoiceId, then retry with the signed payload via _meta or the payment_signature argument). What is missing is any exclusion or explicit routing to alternatives such as get_access_policy_reading when a single domain's current policy is wanted.

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