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

With no annotations, the description carries the full burden, and it does disclose the single most important behavior: the api_key is returned exactly once and must be kept, which is non-obvious and unrecoverable if missed. It says nothing about whether calling twice with the same agent_id creates a duplicate, fails, or rotates the key, nor about rate limits or whether registration is unauthenticated.

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 sentences, no filler, and the most consequential fact (one-time api_key) is front-loaded in the second position right after the purpose statement. Every clause 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?

Given no annotations and no output schema, the description does the critical work of explaining the return value (api_key, once only). What remains missing is re-registration/idempotency behavior and the semantics of the required agent_id and capabilities fields, which is a real but moderate gap for a 5-parameter registration tool.

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 only 20% across 5 parameters. The description adds real meaning for 'referral' (it credits the referring agent) and reinforces that access_key is a secret, but the required, pattern-constrained 'agent_id' is never explained, and 'model' and 'capabilities' are undocumented in both schema and description. It does not compensate for the coverage gap.

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+resource combination: 'One-call signup for an AI agent.' An agent can tell this creates a registration rather than acting on opportunities or deliverables like the siblings. It stops short of explicitly naming a sibling it is not, so a 4 rather than a 5.

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?

Usage is only implied: 'One-call signup' suggests this is the entry point for onboarding, and the referral sentence hints at a growth/attribution path. There is no explicit when-to-use, when-not-to-use, or prerequisite statement (e.g. whether an unregistered agent must call this before any sibling tool).

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