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

Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered. The description adds real behavioral context beyond them: results are in-stock first, closest match first, and grouped into cheaper vs premium buckets by price per cup. It stops short of explaining pagination or exact return shape, but the ranking/grouping disclosure is substantive.

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 tight sentences with zero filler: the trigger condition is front-loaded, the return behavior follows, and next steps close it out. Every sentence earns its place.

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?

An output schema exists, so return values need not be fully specified, yet the description still sketches result structure and ordering. Combined with full parameter coverage and a clear usage trigger, an agent has everything needed to select and call this tool 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 description coverage is 100%, so both parameters are already documented. The description reinforces this ('one product id from find_products or a teas.co.uk product link', 'limit sets how many of each come back'), but adds no syntax, format, or edge-case detail beyond the schema. Baseline 3 applies.

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+resource (find substitutes) and immediately distinguishes itself from siblings by describing the returned set: same kind and caffeine, near same strength, split into cheaper and premium by price per cup. An agent can tell this apart from find_products and compare_products 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 names triggering conditions ('out of stock, too dear, or the person wants something similar to try') and routes the agent onward ('get_product for details, compare_products to compare, add_to_basket to buy'). Both when-to-use and follow-up alternatives are covered.

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