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

Annotations already declare the mutation profile (readOnly=false, idempotent=true, destructive=false), so the bar is lower. The description adds a genuinely useful behavioral fact beyond them: the operation 'adds no entries', i.e. it corrects the stored balance rather than writing ledger records. It does not mention permissions or whether the prior balance is silently replaced, keeping it out of the top band.

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 compact block of sentences, front-loaded with the core semantic ('set what an account holds now') before the formatting rules. Dense but every clause carries formatting or behavioral information; the trailing budget-period note is slightly tangential to the 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 4-parameter mutation with no output schema, the description covers the semantics an agent most needs: unit convention, date format, and the no-ledger-entry behavior. Missing only edge details like auth requirements and explicit overwrite behavior.

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 0%, so the description carries the burden and largely does: it specifies that amounts are integers in minor units with a worked example (45000 = 450.00) and that dates are YYYY-MM-DD. accountId and currency are left implicit but are self-evident from the schema patterns.

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 what an account holds in one currency now) and explicitly contrasts with the ledger-writing siblings by noting it 'adds no entries'. An agent can distinguish this from add_transaction 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?

Frames the tool as 'a correction, like the app's Set balance', which gives clear context for when to reach for it versus recording a transaction. It stops short of naming explicit alternatives or when-not conditions, so it is clear context without full exclusion guidance.

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