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

Annotations already declare readOnlyHint=false and idempotentHint=false, so the agent knows this is a non-idempotent write. The description adds a discovery pointer but says nothing about preconditions (must page/section exist?), failure behavior, or what the returned block looks like; the 'appended by default' behavior is already covered by the position parameter's schema text.

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, zero filler, with the core action stated first and the prerequisite second. Nothing could be removed without losing information.

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?

Output schema exists and annotations plus full schema coverage handle most of the burden, so a short description is defensible for a create operation. The remaining gap is the dangling reference to a schema tool whose name is inconsistent with the parameter description and absent from the sibling list, which is the one thing an agent could trip on.

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% across all six parameters, including the nested 'properties' object and the position default, so the schema carries the parameter burden. The description only reinforces block_type semantics by pointing at the schema tool; it adds no format, merge-order, or valid-value detail beyond structured data.

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: 'Add a new block to a registration site section,' which is unmistakably distinct from update_site_block, remove_site_block and reorder_site_blocks. It stops short of naming those siblings explicitly, so differentiation is inferred from the verb rather than stated.

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?

It gives one useful prerequisite: consult the block-schema tool before choosing block_type. However, it offers no guidance on when to use this versus update_site_block or reorder_site_blocks, and the referenced tool name ('get_site_block_schema') neither matches the schema's own reference ('get_block_schema') nor appears in the sibling list, leaving the agent unsure which call to make.

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