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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), but the description adds a rare and high-value behavioral warning: the upstream `q` parameter is silently ignored and would return the entire 25-million-row platform. This is context an agent could not infer from annotations or schema and directly prevents a costly mistake.

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?

Front-loads the purpose, then the critical no-free-text warning, then sibling routing, then examples — a sensible priority order. It is dense and slightly run-on, but essentially every sentence carries information that changes agent behavior.

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 9-parameter read-only search tool with full schema coverage and annotations, the description covers routing, exclusions, and use cases well. It says nothing about return shape or pagination behavior, and with no output schema that is a minor remaining gap.

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%, so every parameter is already documented in the schema. The description restates the filter axes and gives an example invocation but adds little syntax or format meaning beyond what the schema already provides, so the baseline 3 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?

States a specific verb and resource ('Filter UK planning entities') and enumerates the filter axes (dataset, typology, publisher reference, curie, publishing organisation). It explicitly distinguishes itself from the sibling ukplanning_entities_at_point for place-based designation lookup, so an agent can route correctly without opening either 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?

Provides concrete when-to-use scenarios ('list the conservation areas published by organisation X', 'which entity has reference CA18', 'how many brownfield-land records exist') and names the alternative tool for place-based search. It also states a hard exclusion — that no free-text search is accepted — which is exactly the when-not guidance an agent needs.

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