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

Adds substantial behavior beyond the annotations: the duplicate-detection returns a warning naming the existing ID rather than inserting, costs become expenses tied to the record (Pro-gated), country is resolved and echoed back, and check-out must be after check-in. These are non-obvious mutation semantics the structured fields do not convey.

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?

Front-loads the core purpose and stays dense, but it is a long block and the costs/duplicate guidance runs together. Each clause mostly earns its place, though some of the cost-model explanation could be tightened.

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?

With no output schema, the description helpfully discloses the key return cues (warning with existing ID, echoed resolved country). For a 9-param mutation it covers the critical behaviors, though a few parameters (participantIds, notes, fxRate) remain opaque.

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 11%, so the description carries real weight and does: ISO 8601 with offset for dates, alpha-2/English for country, the costs item shape (amountMinor, currency, category) and the one-line-per-charge rule, plus allowDuplicate intent. Uncovered in either place: city, name, notes, participantIds, spentAt, fxRate, feesMinor.

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 ('Log a new stay') for the authenticated user, and immediately frames its role relative to journeys ('optional accommodation/cost overlay — journeys remain the presence spine'). An agent can distinguish it from log_journey and log_expense from the text alone.

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 concrete when-to guidance: pass costs as one line per charge (fare plus addons/upgrade), use allowDuplicate to override the duplicate guard, and call get_tripledger_guide if unfamiliar. It stops short of naming update_stay as the edit alternative, so no explicit sibling routing for modifications.

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