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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so the safety profile is covered. The description adds two genuinely useful behavioral facts beyond that: it returns URLs rather than file bytes (so the agent must fetch the file separately), and it costs 1 credit per call.

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 short sentences, front-loaded with the core action and return semantics before the pricing and input notes. No filler or repetition of the title.

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 one-parameter resolver with an output schema and full annotation coverage, the description supplies everything needed: what it resolves, that the output is URLs not bytes, and the cost. Nothing material is missing.

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?

There is a single required parameter with 100% schema description coverage, so the schema already documents it fully. The description only restates that url is required and adds no syntax, format, or constraint detail beyond the schema; 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?

States a specific verb and resource ('Resolve a Facebook media URL ... to direct downloadable file URLs') and enumerates accepted media types (image, video, audio) with example sources (post, reel). This clearly separates it from the sibling listing/search tools like facebook_post or facebook_search.

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?

Usage is implied by the scope statement ('e.g. from a post or reel') and by the explicit note that it returns URLs rather than bytes, which tells the agent when this is the right call. However, there is no explicit when-to-use/when-not guidance and no named alternative among the sibling tools.

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