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

Annotations already declare read-only, idempotent, closed-world and non-destructive, so the safety profile is covered. The description adds value the annotations cannot: "Needs no account," which tells the agent no auth setup is required before calling, plus the fact that blocks are self-contained functionality (cookie gating, click-to-load media). It does not say what identifying field the list returns to feed into blocks.get.

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 verb and resource, then value, then the alternative. The middle catalogue sentence is long but each example conveys a capability an agent might otherwise reimplement, so it earns most of its length; a slightly tighter enumeration would read better.

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?

With no output schema and no parameters, the description carries the burden of describing what comes back, and it does so at the level of block types. The one real gap is that it never states the shape of each entry (name/slug/id) that the agent needs in order to call blocks.get afterwards.

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 tool takes zero parameters, so there is nothing to disambiguate and the baseline is 4. The description correctly spends no space on inputs and instead describes output content.

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 ("Lists") and resource ("ready-made building blocks for a site") and immediately enumerates concrete block types, so the agent knows exactly what corpus this returns. It is clearly distinguishable from blocks.get, which is described as retrieving a single block's files.

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 an explicit preference rule ("Prefer a block to writing the same thing yourself") and routes to the sibling that follows this one: "blocks.get gives a block's files, the HTML snippet for the pages and notes." It stops short of a full when-not-to-use statement or a stated call order (list first, then get), so it is strong but not exhaustive.

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