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

Annotations only declare destructiveHint=true, so the description's clarification that this is a partial PATCH and that unspecified fields are left untouched is genuinely additive — it tells the agent unlisted fields will not be cleared. The retirement hint via end_at is another useful behavioral fact. Authorization/prerequisite details and any consequence of changing code text on already-issued tickets are not covered.

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 short sentences, front-loaded with the mutation scope, then the merge semantics, then the retirement recipe and endpoint. Nothing is redundant and no sentence is 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 14-parameter mutation tool with no output schema, the description supplies the two things the schema cannot: partial-update behavior and a retirement workflow. It omits auth/prerequisite context and what a successful or failed update returns, but the rich schema carries the rest.

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 every one of the 14 parameters is already documented with type, bounds, and meaning. The description narrates a few field names (code, value, quantity, validity window, releases) but adds no format, constraint, or interaction detail beyond the schema, which is the correct baseline-3 outcome.

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 (Change) and resource (an existing discount code) and enumerates the editable surface — code, value, quantity, validity window, attached releases — so an agent knows exactly what this tool mutates. It is distinguishable from tito_create_discount_code and tito_get_discount_code by the word 'existing', though it never names those siblings explicitly.

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?

"Only the fields you pass are sent" establishes partial-update semantics, and "To retire a code without deleting it, set end_at to now" gives a concrete workflow for a common intent. No explicit when-not or alternative-tool routing is offered, so it stops short of a 5.

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