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

Annotations already mark the tool as readOnlyHint=true and openWorldHint=true. The description adds useful cost-related behavior: 'Credits: 1 base; hostMedia=true adds +2 per hosted asset (up to 24 / 49 max). Failed assets are not surcharged.' This discloses pricing and failure handling beyond what annotations provide, though it does not mention pagination or rate limits.

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 description is two sentences, front-loaded with the core purpose, then concisely conveying cost details. Every sentence adds value; there is no fluff or redundancy.

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 listing tool with three parameters (all documented in schema) and no output schema, the description covers the purpose, input requirement (URL), and essential cost behavior. It does not explain return format, but since it is a list tool, that is likely self-evident. The hostMedia behavior and credit structure are sufficiently explained.

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 each parameter is documented in the schema. The description adds extra meaning for 'hostMedia' by explaining the credit surcharge and up-to limits, which is not in the schema. This contextual cost information helps the agent decide on parameter values.

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 ('List') and a clear resource ('photos from a Facebook profile or Page'), matching the tool name and title. It unambiguously identifies what the tool does and is easily distinguishable from other facebook_* tools like facebook_profile_posts_list or facebook_post_get.

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?

The description gives clear context: it accepts a profile or page URL and lists photos. There are no competing tools for listing Facebook profile photos, so exclusions or alternatives are not needed. The input requirement is clearly stated, providing enough guidance for when to use it.

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