vault_read_binary

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower, and the description adds real value beyond them: a 4 MiB cap in bytes mode, a signed HTTPS link in auto mode, and a hard PDF exclusion. It does not mention whether signed links expire or require auth, which is the one notable gap.

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?

Front-loaded with the scope statement, then mode behaviors, then the exclusion. Every clause carries information and there is no filler, though the telegraphic style trades a little readability for density.

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?

An output schema exists, so return values need no explanation. The description covers the supported content types, all three modes at least in outline, the size cap, and the PDF exclusion — enough for correct invocation, with only link-mode details and path semantics left implicit.

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 0%, so the description must carry the parameters. It explains the 'auto' and 'bytes' enum values and implies 'link' via the signed-URL mention, but the third enum value is never described on its own and 'path' is undocumented. Partial compensation for a 2-param tool.

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 ('Read images and non-PDF attachments'), which implicitly scopes it away from the text-reading sibling vault_read. It does not name vault_read explicitly, so the sibling differentiation is inferable rather than stated.

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?

It clearly states the negative case ('PDF is unsupported in every mode') and routes PDFs to an alternative ('use the client's native file upload/attachments'), and it describes each 'as' mode. It never says when to prefer auto vs bytes vs link, leaving that inference to the agent.

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