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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world behavior, so the bar is lower. The description adds useful behavioral context beyond annotations: it is a local calculation with no network call, it cites the underlying model (Sandberg, Drexler & Ord 2018), and it explains that unset factors fall back to preset or default values.

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 front-loaded with the core computation, then immediately handles usage and alternatives, then closes with fallback and execution details. Every sentence adds distinct information with no filler.

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?

An output schema exists, so return values do not need full explanation. Given that, the description covers purpose, when to use it, what not to use it for, the alternative sibling tool, default-filling behavior, and local/no-network execution. Nothing essential for correct invocation is missing.

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%, so the schema already defines each factor's meaning and bounds. The description adds value by explaining the relationship between factors, presets, and defaults: 'from your factors or a preset' and 'Unset factors take the preset or default values.' This clarifies optional-parameter behavior beyond the schema.

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 description states a specific verb and resource: 'Compute the Drake equation N (detectable civilisations in the Milky Way)... and the probability that we are alone.' It also explicitly distinguishes itself from the sibling what_did_i_see, so an agent can tell it apart without inspecting the schema.

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?

It gives explicit usage guidance: 'Use it for 'are we alone' and Fermi-paradox questions; it says nothing about UFO sightings (for a light in the sky use what_did_i_see).' This names both the appropriate use case and the alternative tool for adjacent questions.

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