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

Annotations only declare generic safety hints (non-readonly, non-destructive, non-idempotent), so the description must add substance — and it does: it discloses the enforcement behavior on 'buy' and that passing null clears the limit. It does not clarify whether resetting has side effects on pending purchases or whether the limit is checked at bid or delivery time.

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?

A single dense sentence front-loads the actor and action, then layers enforcement and removal semantics without a wasted word. Nothing is repeated from the title or schema.

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 low-complexity two-parameter tool with no output schema, the description covers the core mechanics but leaves the currency dimension open: it never says whether the budget is scoped per currency, what currency is used if omitted, or whether minor units follow ISO 4217 conventions. With annotations covering safety and no output schema to explain, this is adequate but incomplete.

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 0%, so the description carries the burden. It explains the nullable semantics of monthly_budget_minor ('null removes it'), which matches the integer|null type, but the 'minor' unit convention is never defined and the currency enum (chf/eur/usd) — including any default or whether budgets are per-currency — is entirely unaddressed.

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 ('set a monthly spending limit') plus the acting role ('Buyer'), and ties it to the sibling tool 'buy' rather than restating the title. An agent can distinguish this from other set_* siblings (set_mandate, set_delivery_auth) without opening a 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?

Explains the operational consequence ('buy refuses anything above what is left'), which tells the agent both why and when the setting matters, and gives the removal condition ('null removes it'). It lacks an explicit when-not or an alternative tool, but no obvious competing tool exists for this purpose.

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