web_diff

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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely new context: the comparison is a stored fingerprint rather than a fresh fetch, making it cheap, and it names the return shape. It doesn't elaborate on the refetch default/failure behavior, keeping it short of a 5.

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?

Three tight sentences, front-loaded with what the tool does and its outputs, followed by routing guidance and a cost note. No filler and nothing that doesn't earn 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 two-parameter read tool with no output schema, the description names the returned fields (changed, similarity, added/removed blocks), the usage context, and the cost model. An agent has everything needed to select and invoke it correctly.

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 url and refetch (with its default and false semantics) are already documented in the schema. The 'stored fingerprint, not a second full copy' line nudges toward the cached-comparison behavior but doesn't add syntax or format detail beyond the schema, so the baseline 3 applies.

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 ('Compare a page with the copy cached last time and return what changed') and even enumerates the returned fields. An agent can distinguish it from web_watch on the description alone.

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?

Explicitly scopes usage to 'a one-off question of whether a page changed since it was last read' and routes scheduled checking to the named sibling 'web_watch'. This is a textbook when-to-use / when-to-use-something-else statement.

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