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

Annotations declare non-read-only, destructive, non-idempotent, open-world, and the description substantiates each: 'each call adds a new file' explains non-idempotency, 'the file is public under its new URL afterwards' explains the destructive/exposure angle. It adds limits the annotations cannot carry — 3 redirects, 20s per request, 20 MB default with a filter name — plus the safe-URL check, the content-type allowlist with explicit refusals, and the required capabilities (upload_files, edit rights on post_id).

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 purpose and effect before the caveats, and the sentences are information-dense rather than padded. It runs long as a single block, though every clause carries operational detail (limits, allowlist, permissions, return shape) rather than filler.

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?

There is no output schema, but the description supplies the return shape ('{uploaded: true, id, url}'), the security model, the failure modes, and the capability requirements. For a remote-fetch write tool that is everything an agent needs before invoking it.

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 url, title, alt and post_id are already documented, and the description mostly restates them. The one addition beyond the schema is the permission requirement attached to post_id, which the schema also mentions. Baseline 3 applies when the schema does the heavy lifting.

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?

Opens with a specific verb and resource: 'Download a file from a public http(s) URL and add it to the media library.' It also differentiates itself from the near-neighbour wp_upload_media by naming that tool for the base64 case, so an agent can choose between the two 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?

Explicitly routes the alternative case: 'File content at hand is uploaded as base64 with wp_upload_media.' It also states when the tool will refuse (non-public URLs, internal hosts, unsupported content types), which is the equivalent of when-not-to-use guidance.

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