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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds genuinely new behavioral context: this read is agent-internal and has no user-visible effect, which is the key trait distinguishing it from presentation siblings. It stops short of describing failure modes for an invalid target, so not a full 5.

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 tight sentences, zero filler. The core read behavior comes first and the routing alternative is placed last where it is most useful as a decision aid.

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?

Even with no output schema, the description says what comes back (title and markup) and that there is no user-facing side effect. For a one-parameter read tool with readOnlyHint, nothing needed to call it correctly is missing.

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% and there is a single required 'mockup' target parameter, so the schema carries the load. The description implies the parameter identifies a mockup but adds no identifier format, resolution, or scope details beyond the schema.

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+resource ('read a mockup's title and markup') and even scopes what part of the mockup is returned. It explicitly distinguishes itself from the closest sibling, show-mockup, so an agent can select without opening either schema.

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?

Names both the positive condition ('for your own reasoning and for composing edits') and the explicit negative/alternative ('Puts nothing in front of the user — use show-mockup to present it'). The when-to-use and when-to-use-something-else are both spelled out.

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