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

No annotations are provided, so the description must fully convey behavior. It states that it returns null, which is accurate and non-misleading. However, it omits any mention of side effects, idempotency, or safety. For such a simple tool, the description is minimally adequate but not rich.

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?

The description is extremely concise: two short sentences with no wasted words. It is front-loaded with the key behavior. Perfect for a trivial tool.

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 the tool's triviality (no parameters, null return), the description is functionally complete. It could optionally mention its use as a placeholder or contrast with 'true_endpoint'/'false_endpoint', but it is not necessary. The presence of an output schema reduces the need to describe return values.

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 are no parameters, and schema coverage is 100% (empty schema). The description adds meaning by specifying the return value ('null'), which is not in the schema. With 0 parameters, a baseline of 4 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?

The tool name 'null' and description 'Returns null. For when you need a null.' clearly indicate the tool's behavior: it returns a null value. This distinguishes it from siblings like 'true_endpoint' or 'echo' that return other values. However, the description does not explicitly contrast it with alternatives, so it is not a perfect 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?

There is no guidance on when to use this tool versus others. The description only states its purpose, leaving the agent to infer from context. No explicit when/when-not or alternatives are mentioned.

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