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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, and the description goes well beyond them: it flags the April 2026 fee schedule, that outline applications return no fee due to unavailable inputs, that CIL schedules and rates are unverified, and what caveats/sources/next actions accompany the result. That is substantive behavioral context an agent cannot get from structured fields.

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?

Labeled sections (Purpose, When to use, Returns, Limitations, Parameter guidance, Chaining) make it front-loaded and scannable, and every section carries information. It runs long and the Chaining paragraph is slightly verbose relative to its payload, but nothing is truly wasted.

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 6-parameter tool with a nested site_ref object, enums, and an output schema, the description covers triggers, exclusions, parameter conditions, and chaining. An agent has everything needed to decide whether to call it and how to populate the required and conditional inputs.

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?

With 100% schema description coverage the baseline is 3, and the description adds genuine conditional logic beyond the schema: supply address, development_type, and either residential_units for housing or gross_floor_area_sqm for non-residential/change-of-use, plus set application_type when known. It also documents the site_ref chaining contract that the nested object schema only partially conveys.

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 (estimate) and three concrete resources (England planning application fees, CIL coverage/liability, S106 heads) scoped to early feasibility. It also names the sibling it is not (get_local_plan_policies for policy citations), 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?

The 'When to use' block gives explicit trigger phrases (planning fees, CIL, S106, planning obligations, pre-application cost exposure) and names the alternative tool for policy citations. The Limitations block adds real exclusions: no outline estimate, England-only, and it does not replace LPA calculators or legal advice.

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