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

Annotations only declare write/non-destructive/non-idempotent; the description adds substantive behavior the agent could not infer: magic-byte validation against the declared mimeType, the special no-magic-bytes case for text/plain, the 3 MB decoded ceiling, and that the response includes metadata plus a fetch URL. It omits error/duplicate behavior, which is the main remaining 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-loads the core action, then layers constraints and return shape; nearly every clause carries information. The dense em-dash parenthetical on text/plain is slightly hard to parse but not wasteful.

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?

No output schema exists, but the description states what comes back (metadata + URL), and it covers encoding, size, and type validation. Missing prerequisites (permissions, story must exist) and failure modes keep it from fully complete for a 4-required-param mutation.

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 75%, and the description compensates well: it enumerates the accepted mimeType values (schema gives only an example), restates the base64/size contract for data, and clarifies that mimeType must match actual content. filename semantics (display name, extension handling) are still undocumented.

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 ("Upload a file to a story") that no sibling can be confused with; list_attachments/delete_attachment are clearly separate operations. An agent knows immediately what this does.

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 a concrete exclusion with an alternative for oversized files ("larger files: attach them in the Stride app"), which is real routing guidance. It does not, however, say when to upload vs. reference a document, or note prerequisites like story existence or permissions.

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