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

The annotations already declare the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=false, openWorldHint=false), so the bar is lower. The description still adds real behavioral context beyond them by stating 'No email is sent' and sequencing the next call, though it says nothing about what happens when the email already exists or what identifier comes back.

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, each doing distinct work: purpose, scope, side-effect, and next step. The most decision-relevant information (what it creates and the no-email behavior) is front-loaded with 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?

For a two-parameter creation tool with full schema coverage and annotations covering safety and idempotency, the description supplies the essentials. Without an output schema, however, it never says what the call returns (e.g., the user identifier needed by create_app_user_session), which is the one notable gap.

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%, with both email and api_key (including the pro_ vs pub_ distinction) documented in the schema itself. The description adds only indirect meaning through the 'No email is sent' note, so the baseline of 3 is appropriate.

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 a specific verb and resource ('Add an end user to the project') and immediately scopes it with the qualifier about apps where users see only their own records. That qualifier, plus the pointer to create_app_user_session, makes it distinguishable from the similarly named sibling 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?

It gives a clear condition for use ('for apps where each user sees only their own records') and routes the agent to the follow-up tool needed to act as the created user. What's missing is an explicit when-not or a contrast with other creation tools such as create_project or create_record.

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