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

Annotations already establish readOnly, idempotent, closed-world behavior, and the description adds genuinely new operational context: the daily-limit interaction with get_prompt on premium layers and the free-tier escape hatch. The return payload is also summarized, which annotations would not cover.

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, all load-bearing: purpose first, return shape second, cost/limit caveat last. The return-field list is long but each item is distinct schema-less information (no output schema exists), so nothing is 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?

No output schema exists, and the description compensates by enumerating returned fields plus the catalogue-number explanation. For a 6-parameter, all-optional search tool that is close to complete; only the relationship to sibling lookups (get_layer) is left unstated.

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 83%, so the schema carries most of the load (query matching semantics, limit 1-50, offset paging are all documented there). The description still adds value the schema lacks: the catalogue number is the N° shown on tileio.com, and tier "free" means no limit. That is meaningful extra semantics beyond the schema.

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 ('Search the Tileio library by free text and filters') and enumerates what comes back (layer ids, catalogue number, title, category, tier, tone, URL). It clearly reads as a discovery tool, but never explicitly contrasts itself with get_layer or list_targets, so sibling differentiation is only implicit.

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?

Gives actionable context: pass tier "free" to avoid the daily limit, and warns that get_prompt on a premium layer counts toward that limit. It stops short of explicit when-to-use-this-vs-get_layer guidance, but the discovery-vs-fetch split is easy to infer.

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