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

Annotations already flag this as a non-read-only mutation with no destructive intent, so the bar is lower. The description adds the important requirement that each block must be a valid block object and enumerates the accepted types, which helps the agent validate inputs. It doesn't disclose behaviors like uniqueness constraints, ordering guarantees, or error handling, but it adds useful context beyond the annotations.

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?

Two sentences, no filler. The first sentence states the purpose, the second covers block validity and supported types. Every word earns its place.

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 the tool's complexity (19 distinct block types), the schema carries the full burden of field-level detail, and an output schema exists. The description covers the core semantics—append, valid block shape, available types—leaving nothing essential unexplained. The only gaps are optional behavioral notes (e.g., whether block IDs must be unique), but the schema is rich enough to compensate.

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?

The input schema already provides 100% coverage, comprehensively documenting postId and blocks, including a full oneOf discriminator for every block type. The description's phrase '{ id, version, type, data }' adds only a minimal mnemonic; the schema remains the authoritative reference. The 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?

The description opens with 'Append one or more blocks to the end of a post,' using a specific verb and resource that clearly distinguishes it from sibling tools like replace_post_block, remove_post_block, and reorder_post_blocks. The scope is unambiguous and immediately actionable.

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 clearly frames the tool's core use case: adding blocks to an existing post. It does not explicitly contrast with alternative operations (replace, remove, reorder) or state when not to use it, but the context is clear enough for typical appending scenarios, which justifies a 4.

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