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

Annotations cover the safety profile (readOnlyHint=true, openWorldHint=false), and the description adds a genuinely non-obvious behavioral fact — 'Counts as a use' — which is billing/quota information the agent cannot get from annotations. It also describes the payload as a 'full tree', though it does not detail depth or format.

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 sentence plus a short billing note; the core action is front-loaded and every clause carries information (what it returns, the key, the downstream use, the quota cost). 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?

For a no-output-schema, read-only lookup with a fully documented single parameter, the description covers purpose, key, return shape at a high level, and quota cost. It could be slightly more complete about the tree structure or how the result interops with add_nodes node identifiers.

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 only one parameter, so the schema already documents 'Block slug.' The description's 'by slug' adds no syntax or format detail beyond the schema, making 3 the appropriate baseline.

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?

Names a specific verb and resource ('Get a library block's full tree by slug'), which is clearly distinct from listing tools like list_blocks or search_blocks. It also ties the result to a downstream task (hand-building with add_nodes), though it does not explicitly contrast itself with list_block_nodes.

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?

States the context in which to use it: as a reference for hand-building nodes with add_nodes. It gives a clear purpose-driven trigger but no explicit when-not guidance or named alternatives (e.g., when search_blocks or list_block_nodes is preferable).

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