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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds non-obvious context annotations cannot express: the response shape is tier-gated, with Pro/Enterprise returning full_text, source_url, evidence_count and a validation timestamp. It does not cover failure behavior for a stale or unknown UUID, which keeps it below 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?

The INPUT/RETURNS/USE WHEN structure front-loads the operation, then the required argument, then the routing rule. Every sentence carries distinct information; nothing restates the title.

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 read with an output schema and full annotations, the description covers the remaining gaps an agent needs: where the id comes from and that response richness varies by tier. No further detail is required to invoke it correctly.

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 parameter is already documented as a UUID from search_principles results, so the baseline is 3. The description adds provenance semantics — that the id must originate from a prior search call — which is meaningful guidance beyond the schema's format hint.

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 and resource ('Fetch one GEO principle') plus the lookup key ('by its UUID'), which unambiguously separates it from sibling search_principles and bulk_search. An agent can identify the operation without opening 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?

Explicitly states the precondition ('call search_principles first if you do not have one') and the selecting condition ('USE WHEN you already have a principle id and need its full detail — typically to drill down after search_principles'). The alternative path is named, not implied.

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