Head S3 object

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

Annotations already declare readOnlyHint, openWorldHint, and destructiveHint=false, so safety is covered. The description goes beyond that by naming the exact payload returned (size, ETag, content-type, user metadata) and confirming no body transfer, though it omits error behavior (e.g., missing key) and permission requirements.

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?

A single front-loaded sentence with no filler; the key constraint ('without downloading the body') and the returned fields both earn their 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?

With no output schema, the description usefully enumerates the returned metadata, which is exactly the gap it should fill. Error/edge-case behavior is the only missing piece, which is minor for a simple two-parameter read operation.

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 bucket and key are already documented in the schema. The description adds no meaning beyond that (e.g., key format, versioning, prefix behavior), so the baseline of 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 ('Fetch object metadata') and immediately differentiates itself from the body-downloading sibling by specifying 'without downloading the body'. An agent can distinguish this from s3_read_object without opening either schema.

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?

Usage is implied by the 'without downloading the body' clause, which suggests this is the cheap metadata-check alternative to s3_read_object. However, it never explicitly says when to use this versus alternatives (e.g., for existence checks) or when-not to use it.

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