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

Annotations already cover readOnly, openWorld, and destructive=false, so the safety profile is handled. The description adds genuinely non-structured context: the exact response fields returned and the per-request billing cost ($0.003), which an agent needs for cost-sensitive planning.

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 paragraph, front-loaded with the action and accepted inputs, followed by return fields and pricing. The enumeration of return fields is slightly long but each item is informative, so no sentence is wasted.

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 compensates by enumerating the returned fields, and it also discloses the identifier exclusivity constraint and the billing rate. An agent has everything needed to call this correctly.

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%, so the baseline is 3, but the description adds the mutual-exclusivity rule ('provide exactly one of username or url') that is not expressed in the schema itself. This is meaningful semantic value beyond the field-level descriptions.

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 (Get) and resource (Bluesky user's profile) plus the accepted identifier forms (handle, DID, profile URL). It is clearly distinguishable from siblings like bluesky_user_followers, bluesky_user_posts, or search_bluesky_users.

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 a real constraint ('provide exactly one of username or url'), which is useful operational guidance, but it never states when to choose this tool over search_bluesky_users or the other Bluesky profile-adjacent siblings. Usage is implied by the profile-lookup framing rather than explicitly routed.

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