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

Annotations already declare readOnly, idempotent, non-destructive and openWorld, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: the exact payload shape and the 'found is false when no favicon is stored' missing-data signal, which tells the agent how to interpret an empty 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?

One sentence, front-loaded with the action and resource, then the return contents, then the empty-result caveat. Every clause earns its place with no padding, though a semicolon-heavy single sentence is slightly dense.

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 an output schema present, the description needn't document return values in full, yet it still enumerates them, and it covers the empty-result case explicitly. An agent has enough to invoke correctly; only alternative-tool routing is missing.

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?

The only parameter is scan_id and the schema has 0% description coverage, so the schema itself says nothing. The description names the parameter and ties it to the scan scope, but adds no format, source, or validity details (e.g., where scan_id comes from, whether it must be an existing scan). Adequate but thin.

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 ('Get the favicon recorded for a scan_id') and enumerates the returned fields (size, MD5, SHA-256, base64 image), so the agent knows exactly what comes back. It does not explicitly distinguish itself from near-siblings like get_favicon_stats or search_by_favicon/search_favicon_mmh3, though 'recorded for a scan_id' implies per-scan retrieval.

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?

No when-to-use guidance is given. The description never says to use this rather than get_favicon_stats (aggregates) or search_by_favicon / search_favicon_mmh3 (reverse lookup by hash), which are the obvious alternatives in this large sibling set. The scan-scoped nature is only implied by the parameter.

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