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

With no annotations, the description carries the behavioral disclosure burden and does so well: it discloses the 1-credit cost, that empty results and failures are never charged, and the free caching behavior. It does not mention rate limits or auth requirements, but for a read-only fetch tool the cost and caching transparency is substantial.

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 compact and front-loads the core purpose and return content. The cost information is slightly redundant ('(1 credit)' followed by 'Costs 1 credit'), and 'Post thread' is ambiguous as a verb phrase, but the overall structure is efficient.

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?

The description covers the key invocation details: required URL, cache behavior, depth mapping, cost, failure billing, and the main returned fields. With no output schema, it gives enough return-content context for an agent to understand what the tool provides, though it could add explicit sibling differentiation.

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 schema already documents url, cache, and depth. The description adds some context around caching and cost, but it does not add meaningfully new parameter-level semantics beyond what the input schema already provides.

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 it returns a Bluesky post thread via getPostThread and lists the returned content: nested replies, facet links/mentions/hashtags, and rich author info. This distinguishes it from profile and user-post sibling tools, though the phrasing 'Post thread' is terse and could more explicitly say 'retrieve details for a single Bluesky post and its replies.'

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 operational guidance, such as using cache=true for a free 24h cache hit and defaulting to fresh fetches. However, it does not explicitly state when to choose this tool over alternatives like bluesky_profile or bluesky_user_posts, leaving usage context implied rather than explicit.

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