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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds two genuinely useful facts beyond annotations: the credit cost ('1 credit') and the returned fields (views, reactions, comments, shares, video URL). It says nothing about failure behavior for private, deleted, or non-public posts, which matters for an open-world fetch.

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?

A single compact sentence, front-loaded with the resource and followed by the payload fields. Slight redundancy between 'video or reel by URL' and the trailing 'video URL' but no wasted clauses.

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 read tool with no output schema, the description does the needed work by enumerating the return fields and the cost. The remaining gap — private/deleted post handling — is minor but real given the open-world fetch.

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?

With one parameter at 100% schema description coverage, the schema already explains 'url' as a Facebook post, video or reel URL. The description restates the same accepted URL types without adding format examples or normalization rules, so 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 implicitly (fetch) and a specific resource ('One Facebook post, video or reel by URL'), plus the metrics returned. It is clearly distinguishable from list-oriented siblings like facebook_profile_posts or facebook_comments, though it never names them explicitly.

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 only implied by 'by URL' — an agent can infer this is the tool for a single known post permalink. There is no explicit when-to-use or when-not guidance, and no routing to alternatives such as facebook_comments when only comments are needed.

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