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

Annotations already declare readOnly, idempotent, non-destructive, open-world, so the safety profile is covered. The description adds real value beyond that: it bounds the preview to roughly 1,000 characters with short pages returned whole, states no payment is involved, and explicitly warns 'not a safety guarantee', which prevents the agent from over-trusting the result.

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 cost framing ('Free:') is front-loaded and the sentence packs the return contract efficiently, with a compact example at the end. The parenthetical aside about short pages is slightly clunky but still informative rather than redundant.

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?

With no output schema, the description does the necessary work of enumerating what is returned: fetchability, provenance, hashes, injection indicators, and a text preview. What it leaves out is how failures are surfaced (e.g., an unreachable or blocked URL) and whether the preview is truncated by maxChars, which matters for a tool whose name implies a pre-check gate.

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%, so both parameters are already documented, including the maxLength and min/max bounds on maxChars. The description restates the preview limit (which the schema also notes) and gives one example call, but adds no new semantics such as how maxChars interacts with the free preview cap. 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 verb and resource ('checks a public URL') and enumerates what comes back: fetchability, provenance, hashes, injection indicators, and a text preview. An agent can tell it is a non-destructive inspection tool, though it never names the siblings proof_fetch_evidence or proof_fetch_offer to draw the free/paid line explicitly.

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?

'Free' and the name 'preflight' imply this is the cheap check before a paid fetch, and 'No payment or purchase' reinforces that, but the description never says when to use it instead of proof_fetch_evidence or proof_fetch_offer. Usage is inferable rather than stated.

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