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

No annotations exist, so the description carries the full load, and it does well: it discloses three side effects (email link, downgrade to free plan, contribute scope) and a destructive failure mode (five wrong codes invalidate all codes for the key). Remaining gaps are the code expiry window and what a successful response looks like, both of which are left implicit.

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?

Two dense sentences with zero filler: outcome and prerequisites first, failure branch and remediation second. Every clause conveys information an agent needs.

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 and no annotations, the description covers purpose, side effects, failure modes and recovery. Only the success shape and code expiry are absent, which are minor given the disclosed outcomes.

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% for the single parameter, so the baseline is 3. The description adds only that the code is a 6-digit emailed value, which is mildly inconsistent with the schema's 4-12 character bounds and adds little else.

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 ('Confirm the 6-digit code emailed by register or link_email') and names the two sibling tools that produce the code, so the agent knows exactly where this fits. It also names the resulting state changes (links the email, moves the key to the free plan, adds the contribute scope), so the effect is unambiguous.

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 triggering condition (a code was emailed by register or link_email) and the recovery path on failure ('Five wrong codes end every code sent to this key; then call link_email again'). There is no reason to guess when to call this versus link_email.

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