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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered by structured data. The description adds one genuinely new fact (it is free, i.e. no credit cost) and hints at the returned field (project_id), but 'read-only' merely restates the annotation and nothing is said about what the response contains or how ambiguous matches are handled.

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?

Three short sentences, front-loaded with the trigger condition and followed by the practical instruction and cost note; no filler. The closing 'read-only' is redundant with the annotations and is the only wasted clause.

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 zero-param lookup with no output schema, the description supplies the trigger, the key returned identifier, and the cost profile, which is most of what an agent needs. The remaining gap is the shape of the result: whether site names, timestamps, or multiple matches come back, which matters when the person's reference is ambiguous.

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 no parameter meaning for the description to add; baseline for a no-arg tool 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?

The description states the resource (sites/apps the person built earlier) and what the tool yields for the agent (its project_id), which makes the operation's purpose concrete and distinguishes it from build_app/build_site by tying it to a lookup need. It never literally says 'lists all of them' nor clarifies whether the result is one site or many, so the verb is slightly implicit rather than spelled out.

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 an explicit trigger ('when the person refers to a site or app they built earlier'), names the downstream motivation ('for example to publish it'), and adds an ordering rule relative to a sibling ('Call it before offering to build again'). That is exactly the when/when-not routing an agent needs among build_site, publish, and publish_status.

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