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

Annotations cover the safety profile (readOnlyHint=false, idempotentHint=true, destructiveHint=true), and the description adds genuinely non-obvious behavior: omitted parameters retain current values, tax fields are recomputed from the amount, and a Xero-synced record keeps its amount and date. It never explains the `clear` parameter that justifies destructiveHint=true, so the destructive dimension is left only to the annotation.

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?

The purpose and field list are front-loaded, but the passage runs long and includes filler that does not inform the call, notably "exactly as the app does" and the redundant re-explanation that omitted parameters keep current values. Readable, but not maximally economical.

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 an 11-parameter mutation tool with no output schema, it covers the essentials: what can change, what cannot, partial-update behavior, tax recomputation, the organisation guard, and the return value ("the changed record as list_income shows it"). The unexplained `clear` parameter is the main remaining gap.

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 the schema already documents all 11 parameters and the baseline is 3. The description adds framing (partial-update semantics, amount drives recomputed tax) but omits the semantically important `clear` parameter, which is the one case where omitted-vs-cleared diverges.

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?

Names a specific verb and resource ("Changes an income record that is already there") and enumerates the mutable fields, drawing a clear line against create_income and the read-side get_income_record/list_income siblings. It also explicitly carves out the immutable attribute ("Its income type never changes"), which no sibling states.

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?

Gives real operational guidance: "Read the record first, and confirm the change with the person before making it," "Send only what the person tells you," and the organisation gate pointing at list_organisations. It lacks an explicit when-not clause or a named alternative tool for the read step, which would have pushed it to a 5.

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