s3_get_presigned_url

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

Even though annotations already mark destructiveHint=true and readOnlyHint=false, the description adds substantial behavioral context: the URL is a sensitive 'bearer capability' to treat as secret until expiry, the response shape (URL, operation, expiresIn, expiresAt), and the crucial data-flow fact that bytes bypass the MCP server entirely. It also discloses the B2 platform limitation on presigned POST, which an agent could not infer from the schema or annotations.

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?

Five sentences with no filler; the core purpose is front-loaded in the first phrase, followed by usage routing, response/security details, and a constraint note. It is denser than the minimal two-sentence ideal, but each sentence earns its place given the security implications and missing output schema.

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?

Given no output schema, the description compensates by enumerating the response fields. With 7 parameters, the 100% schema coverage handles parameter semantics while the description addresses what an agent cannot infer elsewhere: security handling, expiry behavior, data-path architecture, multipart alternative routing, and a platform-specific limitation. Nothing critical 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?

Schema description coverage is 100%, so the baseline of 3 applies — every parameter already carries its own description. The tool description adds modest framing value by tying expiresIn to the 'short-lived' concept and clarifying that operation selects download vs upload capability, but it does not meaningfully elaborate on versionId, contentType, or confirm beyond the schema.

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 opens with a specific verb and resource: 'Generate a short-lived presigned URL bearer capability for one B2 object', and immediately disambiguates the two modes (GetObject download vs PutObject upload). It differentiates from sibling tools by framing this as URL-based transfer rather than server-mediated access, which separates it from s3_get_object, s3_put_object, and the multipart family.

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?

Explicit routing is provided: 'Prefer this for single-object transfers; use s3_create_multipart_upload and s3_get_presigned_upload_part_url for multipart uploads.' It also states this is 'the preferred path for moving real object data' and gives a hard exclusion (presigned POST unsupported by B2, use PutObject URL instead). An agent receives clear when-to-use and when-not-to-use guidance with named alternatives.

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