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

Annotations already declare readOnlyHint=false, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description adds the useful 'already hosted' precondition and the video-job workflow, but omits what happens to existing media on the post and whether the post must be in a particular state.

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?

Two tight sentences plus a docs link, with the core action front-loaded and the workflow hint second. Nothing is wasted, though the trailing docs URL adds little for an agent.

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?

For a mutation tool with no output schema, the definition covers the action and a typical workflow but leaves behavioral gaps (media replacement semantics, post-state requirements, error behavior). Annotations cover the non-destructive/open-world profile, so this is adequate but not complete.

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 67% – url and idempotencyKey are documented in the schema, while postId has no description. The description adds no parameter-level detail beyond the schema, so the baseline 3 applies.

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 (add a hosted image/video URL to an existing post), and the phrase 'already hosted' meaningfully separates it from upload_media and import_media. It never names those siblings explicitly, so the differentiation is inferred 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 gives a concrete when-to-use scenario (create post, generate video, then attach) which is genuinely helpful sequencing for an agent. However it offers no exclusions or explicit pointers to alternatives such as upload_media for non-hosted files.

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