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

readOnlyHint=true already declares the safety profile, lowering the bar. The description adds genuine behavioral context beyond the annotation: the tool analyzes 10 specific SEO dimensions and optionally captures screenshots of both pages, implying a heavier fetch-and-render operation. It does not disclose return format or failure behavior for inaccessible URLs, but the annotation covers the core safety concern.

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?

Two sentences with zero filler: the primary action and scope are front-loaded, the criteria are packed into an efficient enumeration, and the optional screenshot behavior sits at the end. Every element earns its place.

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 tool with no output schema, the description gives no hint of the return format — an agent cannot tell whether screenshots are returned as URLs or data, or whether the comparison comes back as a table or structured report. Prerequisites (both URLs must be publicly accessible) and error behavior for one failing URL are also unaddressed. The full parameter schema and readOnly annotation compensate partly, but the missing return-value context is a real gap.

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 the baseline of 3 applies — urlA, urlB, and includeScreenshot are already documented with useful descriptions including the JPEG quality 60 detail. The description's mention of 'Optionally captures screenshots' is redundant with the schema's includeScreenshot description, adding no new parameter meaning.

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 — 'Compare two web pages side by side' — and enumerates the exact SEO criteria (title, meta description, headings, word count, links, images alt, Open Graph, Twitter Card, JSON-LD, canonical). The two-page comparison scope clearly distinguishes it from the 30 siblings, none of which perform side-by-side comparison.

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?

The use case is implied by the description: call this when you need a side-by-side SEO comparison of two pages. However, there is no explicit when/when-not guidance or alternative routing, e.g., no 'for a single-page audit use audit_onpage' or 'for screenshots alone use screenshot', despite those siblings covering overlapping functionality.

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