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

Adds real constraints beyond annotations: accepted formats, 10 MB, 32 megapixels, 8000 px per dimension, and the important clarification that uploading does not mutate a post. Annotations already cover safety (readOnly=false, destructive=false, idempotent=false, openWorld=true), so the description's job is narrower and largely done; it stops short of stating failure/duplicate-name behavior or 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?

Three dense sentences: capability and constraints first, parameter selection second, return value and scope limitation last. No filler or redundancy.

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 yet the description explains the return value (url) and its intended consumers. Combined with the format and size limits and the explicit scope statement, an agent has everything needed to call this correctly on the first try.

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 requires nothing (required: []) and only half the properties carry descriptions, so the description carries the load: it declares that exactly one of file/source_url must be supplied, and the size/format limits apply to both paths. This is information the schema alone would not convey.

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 one JPEG, PNG, GIF or WebP image') and immediately scopes the destination ('to the connected blog'). Explicitly distinguishes its scope from sibling mutation tools by noting 'Uploading alone does not edit or publish a post.'

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 the exact selection rule between the two parameters ('exactly one is required') and downstream usage ('Returns url for content.featured_image_url, gallery images or HTML'). Also names the exclusion that prevents confusion with create_content/publish_content.

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