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

Annotations already declare readOnlyHint=false, idempotentHint=false and destructiveHint=false, so the agent knows this is a non-idempotent side-effecting action. The description adds that an email is actually dispatched and that the code is one-time, which is genuinely useful context beyond the annotations, but it omits rate limiting, code expiry, and whether requesting a second code invalidates the first.

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?

A single sentence with the action and resource front-loaded and zero filler. The parenthetical efficiently carries the workflow linkage without a second sentence.

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 one-parameter tool with no output schema this is close to sufficient, and the annotations cover the safety profile. Still missing for correct invocation: what happens after the code is emailed, code validity/expiry, and error behaviour for an unrecognized email address.

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?

There is only one parameter and schema description coverage is 100% ('Your partner email.'), so the schema already carries the full parameter burden. The description adds no syntax, format or constraint information beyond what the schema provides; baseline 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?

States a specific verb and resource — email a one-time sign-in code to a partner account — and names the sibling tool partner_signin in the parenthetical, so the agent can distinguish this code-delivery step from the sign-in step itself. It is clear but the differentiation is embedded in a parenthetical rather than stated as a routing rule.

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?

The parenthetical 'for a new API key with partner_signin' implies the workflow context (call this to obtain the code that partner_signin consumes), which is useful implied usage. However, there is no explicit when-to-use vs. when-not statement, no prerequisite (existing partner account) and no note on what to do if a code was already requested.

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