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

Annotations indicate readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false. The description adds significant context beyond these hints: it discloses the on-demand fetch queue with ~90 second readiness, jobRef polling, CDN URL expiration, YouTube's thumbnail-only return, and credit cost. It also warns about legal responsibility, which is valuable operational context.

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?

The description is appropriately sized for the tool's complexity, front-loaded with the primary purpose. It covers necessary caveats (CDN expiration, YouTube thumbnail, legal, cost) without fluff. While dense, every sentence carries relevant information.

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, so the description must explain return behavior. It mentions direct media URLs, jobRef for polling, and thumbnail for YouTube. It also covers the fetch flow and credit cost. It could explicitly describe the response structure for media URLs, but the description gives sufficient operational detail for an agent to use the tool correctly.

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%, with both parameters already described in the schema. The description repeats the alternative nature of url/postId but adds no new meaning beyond the schema. Baseline 3 applies because 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?

The description clearly states the tool returns direct media URLs for a tracked post, video file, or slideshow images with positions. It uses a specific verb ('returns') and resource ('media URLs') and distinguishes from sibling tools like get_post by focusing on media download.

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?

The description explains when to use the tool: to get media for a tracked post, accepting either a public URL or internal post ID. It also describes the on-demand fetch flow and advises to call again once complete. However, it does not explicitly mention alternatives or exclusions, though the context implies the tool is for media downloading rather than general post retrieval.

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