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

Annotations already cover readOnly/openWorld/non-destructive, but the description adds genuinely non-derivable behavior: pinned-post-first then newest-first ordering, up to 50 posts per page, and $0.003 per-page billing. Cost disclosure is especially valuable and is not in any structured field.

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?

One dense sentence plus a short returns/pricing clause; the input constraint is front-loaded, ordering and output shape follow, and pricing closes. No filler.

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 carries the return burden and does so: post text, engagement metrics, media, link cards, quoted posts, and is_reply/is_repost/is_pinned flags, plus pagination and cost. Nothing essential to calling it correctly is missing.

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 baseline is 3, and the description earns a bump by adding the mutual-exclusivity rule ('exactly one of username or url') that the schema does not express. Per-page billing semantics reinforce the pages parameter.

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 ('Get a Bluesky user's feed') and scopes the content precisely: posts, replies, reposts, with ordering. It implicitly distinguishes itself from post-level siblings like bluesky_post_details, but never names an alternative, so an agent must infer the boundary.

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 parenthetical 'provide exactly one of username or url' is a real input constraint, but there is no when-to-use guidance versus siblings such as bluesky_user_profile, search_bluesky, or bluesky_user_likes. Usage is implied rather than stated.

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