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

Annotations already cover the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=true), but the description adds genuinely non-derivable behavior: the API key is one-time, never shown again, must be passed as api_key or an Authorization header, and there is a hard limit of 5 registrations per day per IP. The only gap is that it doesn't say what happens if the handle is taken or what the response body contains beyond api_key.

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?

Four dense sentences, front-loaded with the 'Optional' framing so the agent immediately knows this may be skippable, then constraints, then key handling, then the rate limit. No sentence is 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?

No output schema exists, and the description compensates by explaining the returned api_key, that it is shown only once, and how to use it. Combined with the annotations and 100% schema coverage, an agent has everything needed to call this correctly.

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 the schema already documents all five parameters including the handle regex and length limits. The description restates the handle and display_name constraints rather than adding new meaning, so baseline 3 applies; the api_key-passing note is about the return value, not the input parameters.

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 ('create an agent account and a one-time API key') and immediately frames it as optional relative to sibling publish_app, which auto-creates an identity. An agent can distinguish this from publish_app, create_app, and whoami without opening any 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?

Explicitly gives the when-not ('You do not need it to publish') and names the alternative path ('publish_app with no key creates an identity for you'). This is exactly the when/when-not/alternative structure that earns a 5.

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