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

Annotations only declare readOnlyHint=false and destructiveHint=false; the description adds meaningful context beyond that — the token arrives via email, it is the sole proof (no separate code), and a session must exist first. It does not disclose token single-use/expiry semantics, so not a full 5.

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 short, front-loaded paragraphs with no filler; the core action leads and the access requirement follows. The redundant re-statement of the token's email origin is the only slight cost.

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 single-parameter verification tool with no output schema, the description covers the action, the credential source, and the prerequisite session/auth flow. It doesn't state what success yields (session established vs. challenge cleared), a minor gap for a tool whose whole point is a state change.

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 coverage is 100% and the single token parameter is fully documented ('Magic link token from the verification email'). The description's 'received via email' phrasing largely restates the schema, adding no format or source detail beyond it — baseline 3.

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?

Specific verb + resource ('Complete a 2FA challenge using a magic link token'), plus a clause that separates it from sibling code-submission tools: 'No code submission needed — the token itself is the proof.' An agent can route between this, verify_2fa, and submit_verification_code without opening schemas.

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 ACCESS paragraph gives concrete when/how-to-use guidance (needs a Proof account; authenticate via /mcp or start_login, then call again), which is real operational routing. It stops short of explicitly naming an alternative for the code-based path (verify_2fa), leaving that contrast implied rather than stated.

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