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

Annotations already provide readOnlyHint, idempotentHint, openWorldHint, and destructiveHint=false, so the description doesn't need to restate that this is a safe read. It does add behavioral context about filtering by "non-expired" and "most recent" snapshots, which are useful beyond the schema, but it doesn't describe what happens if no snapshot exists or whether the response is singular/null.

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 convey a complete, front-loaded purpose. The first sentence explains the operation, and the second sentence adds relevant usage guidance without unnecessary filler or redundancy.

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 one-parameter, read-only retrieval tool with no output schema, the description is adequate: it states the action, the freshness constraint, and relationships to two sibling tools. It does not cover edge cases like missing/expired snapshots, but those are not essential for a correct call and the annotations cover safety. A small gap is the lack of any indication of the result shape, but no output schema exists to fill that.

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%: the only parameter 'url' is described as "The URL to look up (must match the URL used when the test was run)." The description adds only "single URL" and the notion of freshness, which are largely already implied. It does not need to compensate for schema gaps, so the 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?

The description states a specific verb and resource: "Get the most recent non-expired test snapshot for a single URL." It also distinguishes itself from siblings by explicitly mentioning gvt_get_oldest and gvt_get_score_trend, making its role clear without needing to inspect other schemas.

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?

Gives explicit instructions on how to use this tool: combine with gvt_get_oldest to compare baseline vs current, or use gvt_get_score_trend for a pre-computed comparison. This directly guides the agent through its main decision points and names the alternatives.

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