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

Annotations already declare readOnly/openWorld/idempotent, so the safety profile is covered; the description adds real value beyond that by disclosing the timeout behavior for unscoped searches and the concrete return payload (registry ID, coordinates, county FIPS, per-program flags, five-year inspection and penalty totals, TRI release totals). Pagination and the default limit are left to the schema, which is why this is not a 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?

Four sentences, each carrying distinct information, with the purpose and the payload front-loaded before the operating constraint. No restatement of the tool name or 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?

For a 10-parameter read-only search with 100% schema coverage, full annotations, and an output schema, the description covers everything remaining: scope, the return fields, the hard filter requirement, the single-program limitation, and the handoff to epa_echo_get_facility. Nothing an agent needs to call this correctly is absent.

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 the baseline is 3, but the description adds semantics the schema can't: that a program filter accepts only one value per search, and that latitude/longitude/radius_miles must be supplied as a complete triple. It also frames the geographic filters as a required disjunction, which is a cross-parameter constraint the schema doesn't express.

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?

Names a specific verb (search) plus resource (EPA-regulated facilities) and enumerates the filter axes (location, program, compliance status) and covered programs (CAA, CWA, RCRA, TRI, SDWA). It also distinguishes itself from the sibling epa_echo_get_facility by explaining that the returned Registry IDs feed that tool, so an agent can route between them 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?

Explicitly states the hard precondition that at least one geographic filter (zip_code, state, city, or a complete lat+lon+radius triple) is required and that unscoped searches time out, which is exactly the kind of routing rule an agent needs. It also explains the proximity-search path. What's missing is guidance on when to use this versus epa_echo_search_violations, given that has_violation overlaps with that sibling's purpose.

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