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

Annotations already declare destructiveHint=true, idempotentHint=true and openWorldHint=true, so the safety profile is covered. The description adds two behaviors the annotations do not: merge semantics (passed fields are merged into existing block data rather than replacing it) and immediate public visibility requiring user confirmation. Auth/rate-limit context is not added, which is acceptable given 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?

Roughly four sentences with no filler; each carries scope, data source, merge behavior, or the confirmation warning. The action statement sits in the third sentence rather than the front, which slightly weakens front-loading, but the closing warning is correctly placed last.

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 mutation tool with full annotation coverage, 100% schema coverage, and no output schema, this covers what an agent needs: where blockId comes from, that data is merged, that edits go live immediately, and that the user should confirm. The scope note that no purchase occurs in chat usefully rules out checkout-type siblings.

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 coverage is 100%, so the baseline is 3, but the description adds real meaning beyond the schema: 'merge' clarifies that 'data' is a partial update rather than a full replacement, and it points to add_store_block for the per-type shape definition. It does not address workspaceId or idempotencyKey, which the schema already documents.

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 operative sentence — 'Merge the fields you pass into a block's data' — names a specific verb (merge), resource (block data), and distinguishes this from add_store_block and delete_store_block. The opening store-administration framing is scope context rather than purpose, but the action itself is unambiguous.

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?

Gives concrete prerequisites: blockId comes from list_store_blocks and data mirrors add_store_block, and it states the key usage directive 'Public at once: confirm with the user.' It does not name alternatives for related operations (reorder_store_blocks, hide_store_block, delete_store_block), so exclusions are absent.

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