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

The only annotation is destructiveHint=true, so the description usefully adds the side-effect disclosure that this is 'Additive — sends no notification,' plus the underlying endpoint (POST /users). It does not cover what happens if the user already exists or any auth/permission requirements, which would have raised this further. Note the mild tonal tension with destructiveHint=true, but 'additive' describes lack of side effects on other resources rather than contradicting a write operation, so this is not a contradiction.

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, no filler, with the core action and the non-obvious 'no notification' behavior front-loaded ahead of the constraint and endpoint. Every sentence earns its place.

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 7-parameter mutation with no output schema and only a destructiveHint annotation, the description covers action, side effects, the minimum-identifier rule, and the API route. The main remaining gap is the outcome of the call (duplicate/existing-user behavior and what the response contains), which an agent would otherwise have to discover at runtime.

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 baseline is 3 and the schema carries field-level meaning. The description goes beyond it by stating the cross-parameter constraint that at least one of external_id or email must be supplied — genuinely necessary information since the schema marks nothing as required.

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 ('Creates a user record in MagicBell') and parenthetically explains what a user is in this domain ('notification recipient'), which is not inferable from the name alone. The verb cleanly separates it from siblings like magicbell_get_user, magicbell_list_users, and magicbell_update_user.

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 one actionable precondition — 'Provide at least one identifier (external_id or email)' — which the schema does not enforce (required count is 0). However it never states when to prefer this over magicbell_update_user, nor whether calling it for an existing user is idempotent/upserting, so alternative selection is left to inference.

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