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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so safety is covered. The description adds genuinely useful behavior beyond that: replies are returned up to 10 levels deep as a flat list of full posts whose in_reply_to_id points at the parent, plus a concrete cost of $0.003 per request.

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?

Three tight sentences, front-loaded with the action and identifier rule, followed by return shape and cost. Every sentence carries distinct information with 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 compensates by describing the return shape (flat list of full posts with in_reply_to_id pointing at the parent), the traversal depth, and the per-request price. An agent has everything needed to call it correctly and predict the response.

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 url or post_id) that the schema itself does not state, which is meaningful invocation guidance.

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 the replies to a Bluesky post') and specifies the two accepted identifiers (URL or AT URI post_id), which distinguishes it cleanly from siblings like bluesky_post_likes, bluesky_post_quotes and bluesky_post_reposts that target the same parent post.

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 implied by the verb and resource, and the 'provide exactly one' constraint tells the agent how to supply identifiers, but there is no explicit when-to-use/when-not guidance or named alternative for retrieving related post data.

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