Get object metadata without downloading its content

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

The annotations already declare readOnlyHint=true and idempotentHint=true, so safety is covered. The description adds behavioral context by explaining that the body is not transferred and enumerating the metadata returned (content-type, size, etag, last-modified, user metadata), which is valuable given there is no output schema.

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 the primary action in the first sentence and cost guidance in the second. All words are informative; no 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?

The description covers purpose, behavior, return value (metadata fields), and the cost tradeoff vs. the main alternative. Given no output schema and a simple HEAD operation, this is sufficient for an agent to select and invoke the tool 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 descriptions cover 100% of parameters (bucket, key, region with defaults and enum), so the description need not repeat them. The tool description adds nothing beyond the schema for parameter semantics, so 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?

The description uses a specific verb ('Fetch') with a clear resource ('object metadata') and explicitly states that it does not transfer the body, distinguishing it from the sibling tool scaleway_s3_get_object. The title reinforces this by stating 'Get object metadata without downloading its content'.

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 description explicitly compares to scaleway_s3_get_object: 'Cheaper than scaleway_s3_get_object when you don't need the content.' This gives a concrete when-to-use condition and names the alternative tool.

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