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

Annotations only declare readOnlyHint/openWorldHint, and the description goes well beyond them: it discloses breadth-first walk order, per-node depth and parent tagging, a cost cap, and truncation behavior. It also flags a real limitation — the descendant tree assumes the app.bsky.feed.post lexicon and will be empty for record types modeling replies differently. That is strong disclosure, though it leaves pagination/cap values unquantified.

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?

Front-loaded with the core behavior before caveats and alternatives; every sentence carries information. It is dense and slightly run-on (comma-spliced clauses around 'replies, replies-to-replies'), which costs a point on readability.

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?

Given an output schema exists, return shape needn't be explained, yet the description still conveys the node structure (depth, parent) an agent must reason about. Behavior, lexicon caveat, and truncation escape hatch are all present; nothing needed for correct invocation 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 description coverage is 100% and there is a single parameter, so the schema already documents the URI format. The description's 'Input is a post's at:// URI' restates rather than extends the schema, so baseline 3 applies.

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 (reconstruct) and resource (the conversation around a post), then precisely scopes it: ancestor chain to root plus a bounded descendant reply tree. An agent can distinguish it from get_backlinks or list_backlink_records without opening a schema.

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?

Explicitly names the user question it answers ('show me this whole conversation / what is this replying to?') and routes to a specific alternative (list_backlink_records on a post URI) when the tree is truncated. Both the use case and the escalation path are covered.

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