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

Annotations already declare destructiveHint=true and idempotentHint=false, but the description adds value the annotations cannot: the write propagates into expense and profit-and-loss reports, and the auth requirement is a Read/Write key. The duplicate-on-retry warning restates idempotentHint=false, so it is useful but partially redundant.

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?

Three short sentences, no filler, with the WRITE marker and the core purpose front-loaded before the side effects, the auth requirement, and the endpoint. Every sentence adds a distinct operational fact.

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?

Covers purpose, auth, side effects, and duplicate risk for a ten-parameter mutation with no output schema, leaving the schema to document the remaining fields. Minor gap: it lists date among the core inputs even though expense_date is optional and defaults to now, and it says nothing about the optional category/location fields that shape reporting.

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 explains every one of the ten parameters, including defaults for expense_date and the location_id cross-reference. The description only echoes description/amount/date and adds no constraints, formats, or mapping beyond that, making the baseline 3 appropriate.

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 ("record an expense in the store's books") and names the core content inline (description, amount, date). The "WRITE:" prefix and the POST /expenses endpoint immediately separate it from the read siblings like phppos_list_expenses and phppos_get_sale.

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 a concrete prerequisite ("Needs a Read/Write API key") and routes the agent to phppos_list_expenses before retrying, which is real decision guidance. It stops short of stating when an expense should not be recorded or when a different creation tool applies, so it is strong but not exhaustive.

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