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

Annotations already declare readOnlyHint=false, destructiveHint=false, and idempotentHint=true, so the safety profile is covered. The description adds the ownership constraint and the conflict outcome of the compare-and-set guard, which is genuine extra context, but it says nothing about which fields are mutable, whether omitted fields are left untouched, or what happens on validation failure — notable gaps for a mutation tool.

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?

One short sentence, front-loaded with the verb and resource, with no filler or repetition. It is efficient, though the extreme brevity borders on under-specification rather than tightness.

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?

A 7-parameter mutation tool with low schema coverage and no output schema needs more than one sentence. An agent cannot tell which budget attributes are updatable, what units monthly_limit_cents or alert_at_pct use, or what a partial update leaves unchanged — all left unaddressed.

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 only 29%: only id and expected_updated_at are documented. The description mentions expected_updated_at, but that parameter's semantics (CONFLICT behavior) are already fully spelled out in the schema. The five undocumented fields — currency, is_active, category_id, alert_at_pct, monthly_limit_cents — receive no explanation of valid ranges, units, or effects anywhere, and the description does not compensate.

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 ("Update a expense_budget") plus an ownership scope, which clearly distinguishes it from expense_budget_create, expense_budget_read, and expense_budget_list. It stops short of naming a sibling or routing rule, so it is clear but not maximally differentiating.

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?

The parenthetical hints at when to supply expected_updated_at (compare-and-set), and "you own" implies a precondition. However, there is no explicit when-to-use vs when-not guidance, no mention of how partial updates are treated, and no pointer to expense_update or expense_budget_read for the read side.

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