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

Annotations already declare idempotentHint=true, destructiveHint=false, readOnlyHint=false, openWorldHint=false, covering the safety profile. The description adds the ownership requirement and points at the CAS conflict behaviour, but says nothing about patch semantics (whether omitted fields are cleared or preserved) — a material gap for a 14-parameter mutation.

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 compact sentence with the resource and the CAS option front-loaded; nothing is padded. The minor grammar slip ('a expense_recurrence') is the only blemish.

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 mutation with 14 parameters, 14% schema coverage, and no output schema, the description is far too thin — it should at minimum state patch vs. replace semantics, which fields are mutable, and what the CONFLICT response means for the caller's next step.

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 only 14%: just 'id' and 'expected_updated_at' are documented in the schema, and the description only elaborates on expected_updated_at. The twelve other fields (amount_cents, frequency, is_active, day_of_week, day_of_month, total_generated, last_generated_at, etc.) get no semantics in either place, and the critical question of whether this is a partial or full replace is unanswered.

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 ('Update') and resource ('expense_recurrence') and adds a scope constraint ('you own'), which distinguishes it from the read/create/delete siblings. It does not explicitly name alternatives, but the verb makes the family distinction obvious.

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?

Implied usage only: update an existing recurrence you own, with an optional compare-and-set mode. There is no explicit guidance on when to use this versus expense_recurrence_read-then-update, nor exclusions or prerequisites beyond ownership.

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