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

Annotations already establish readOnly, idempotent, and non-destructive hints. The description adds concrete behavioral context: it returns a single principle with specific fields, and notes tier-dependent additional fields. This goes beyond the annotations without contradicting them.

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?

Three sentences, front-loaded with the primary purpose, then logically structured with INPUT, RETURNS, and USE WHEN. Every sentence provides distinct value with no redundancy.

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 simple single-param fetch tool, the description fully covers the use case, return format, tier differences, and typical workflow. An output schema exists, so return values need no elaboration, but the description still supplies it. No gaps in necessary context.

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?

The input schema already documents id with 'Principle UUID (from search_principles results)' at 100% coverage. The description repeats this and adds 'normally taken from a prior search_principles result,' a minor enrichment. Baseline 3 is justified because the schema carries the semantic weight.

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 opens with 'Fetch one GEO principle from the Proximens GEO Engine by its UUID,' naming a specific action (Fetch), the resource (one GEO principle), and the identifier method (UUID). This clearly differentiates it from siblings like search_principles or get_stats.

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 description explicitly states 'USE WHEN you already have a principle id and need its full detail — typically to drill down after search_principles.' This provides strong contextual timing but does not explicitly list alternatives or when-not-to-use scenarios, so a 4 is appropriate.

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