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

The annotations only declare readOnlyHint and openWorldHint; the description adds that this reads the logged-out public view (implying no auth and only publicly visible reels), that the fetch goes through a residential proxy from facebook.com, and that billing is $0.01 USDC per successful call via x402 with failed calls free. Those cost and access-path details are exactly the kind of context annotations cannot carry. It omits rate limits and latency, which keeps it from a 5.

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 purpose and input are front-loaded, which is good, but the field enumeration duplicates what the existing output schema already declares, and the trailing block packs proxy, related-tool, and pricing details into one dense run-on. Every clause is defensible but the field list is redundant given the output schema.

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?

With an output schema present, the description need not explain return values, and it still covers access scope, input forms, cost model, and sibling alternatives. Nothing essential for a correct single-parameter read call is missing; only failure modes (private/deleted reels, geo-blocking) are unaddressed.

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 100% and the single parameter already documents accepted forms ('Reel link (facebook.com/reel/<id>) or numeric reel id'). The description's 'Input a reel link or id' restates the schema rather than adding format or edge-case guidance, 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?

States a specific verb and resource (fetch Facebook Reel details from the public reel page) and enumerates exactly what comes back: title, caption, duration, thumbnail, owner, post time, and reaction/comment/share counts. It also names two sibling tools it is not (social_facebook_followers_following, social_facebook_page_contact_info), so an agent can route correctly without opening any 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?

Gives an explicit alternative-selection rule for its named siblings ('when you need Facebook Page follower counts...', 'when you need contact details from a Page's About tab'), which is genuine when-to-use guidance. It stops short of stating when *not* to use this tool (e.g. private reels, unavailable regions), so it is clear context rather than full exclusion logic.

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