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

Annotations already declare readOnlyHint/idempotentHint/destructiveHint=false, so 'Read-only, no key' mostly restates them (though 'no key' does add auth context). What earns credit is genuinely new behavior: the 20-entry cap, the 'entries: [] with ledger_status not_yet_covered plus covered symbols' edge case, and the explicit paywall boundary that payload bytes are the separate paid derivation_replay product. That is material disclosure an agent could not infer from the annotations.

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 core purpose and organized by mode (with symbol / without symbol / read-only), with no filler sentences. It is on the long side for one optional parameter, but each sentence contributes a distinct fact (fields returned, truncation limit, empty-result status, paywall boundary).

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?

There is no output schema, and the description compensates fully: it enumerates the returned fields (time, verify_url, SHA-256, size, collector code hash, fetch status), describes the coverage-list shape, and handles the not_yet_covered edge case. An agent has everything needed to call it and interpret the response.

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% and the single optional param already documents case-insensitivity and that omitting it returns the coverage list. The description adds the 'up to 20 recent fetches' limit, but that is return-volume behavior rather than parameter semantics. Baseline 3 is right when the schema carries the parameter documentation.

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+resource ('Returns the derivation ledger index') and then cleanly splits the tool into its two operating modes: with a symbol (up to 20 archived upstream fetches) and without (coverage list). It also names the sibling it is not — 'To compare a live value with its upstream right now, use verify_value' — so an agent can separate it from verify_value and verify_footprint 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 routing: supply a symbol to trace one published value to bytes/build, omit it to get the coverage list. It also names verify_value as the alternative for live comparisons, which is the main confusion risk among the verify_* siblings. When-to-use and when-to-use-something-else are both covered.

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