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

Annotations already carry readOnlyHint=true, openWorldHint=true and destructiveHint=false, so safety is covered; the description adds real value with the returned field list (photo_id, accessibility_caption, viewer_image uri/height/width, thumbnail, url) and the warning that 'Repeated requests may purchase data again'. However, the cost statements contradict each other inside the same description ('at least 10 Nexscope credits' versus '1 credit per request'), which leaves the agent with an unreliable picture of the billing impact of a 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?

The core is front-loaded, but the text is padded with scraped copy: 'Facebook Profile Photos API View Pricing Get a public Facebook page's photos.' repeats the purpose sentence verbatim, the credit cost is stated three times with conflicting figures, and 'Examples are not guaranteed prices' is boilerplate. Several sentences do not earn their place and one actively misleads.

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 no output schema, the description correctly carries the burden of describing return fields and the pagination loop, which it does well. What is missing is a coherent cost model and any note on limits or what an empty/invalid page URL returns. For a simple 3-parameter read tool, it is adequate but undermined by internal inconsistency.

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%, so the baseline is 3 and the schema already documents all three parameters. The description does add one genuinely non-obvious detail beyond the schema: next_page_id and cursor must be passed together and both must come from the previous response. That is incremental value, not a rewrite of the schema.

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 opening sentence states a specific verb and resource: 'Fetches photos from a public Facebook page'. That distinguishes it from the nearby siblings social_facebook_profile_posts, social_facebook_profile_reels and social_facebook_profile_events, though it never names those alternatives explicitly. The purpose is unambiguous, but sibling routing is left implicit 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?

Usage context is only implied: the tool targets 'a public Facebook page' given a page URL, so a private profile or a post-level lookup is out of scope, but the description never says so or points to a different tool for those cases. The pagination instruction ('Pagination requires passing both next_page_id and cursor from the previous response') is useful procedural guidance but not when-to-use guidance.

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