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

Annotations already cover readOnly, idempotent and non-destructive, so the bar is lower; the description adds real value by disclosing that the call 'Counts as a use', a metered/quota consequence not visible in structured fields. It also implies the return payload is Liquid source. No mention of failure behavior for unknown slugs.

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 front-loaded sentence plus a short usage caveat; every clause carries information (resource, key parameter, purpose, exclusion, billing implication). 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?

With no output schema, the description helpfully names what comes back (Liquid code) and what it is for. It does not address pagination, error cases, or whether site scoping via id changes resolution, which are the remaining gaps for a read tool of this kind.

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%, so both parameters (id, slug) are already documented in the schema. The description only echoes that lookup is by slug and adds no format, scoping, or precedence guidance beyond it — 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?

States a specific verb and resource: retrieves a library block's Liquid source by slug. It also disambiguates from template-application siblings by saying it is 'a reference for writing your own section, not a default to place', which immediately separates it from apply_kit_block-style tools.

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?

Tells the agent the intended use — inspect an existing block as a reference when authoring your own section — and warns against treating the result as something to drop in. It stops short of naming the alternative sibling to use for actual placement, leaving that inference to the agent.

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