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

Goes well past the readOnly/openWorld annotations: it discloses that savings are ESTIMATED and never realised, that every figure is labelled LIVE, INDICATIVE, HISTORICAL or ESTIMATED, the exact endpoint, that it consumes a shared allowance, and that analysis_id lets you read a kept analysis instead of computing. These are the confidence and cost traits an agent needs before quoting numbers to a user.

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-loaded with the value proposition and tightly packed, with each clause carrying information. It does repeat the confidence caveat ('ESTIMATED, never realised' and 'estimated savings are never realised'), which is redundant in a paragraph this short.

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 15-parameter tool with a nested object and no output schema, the description names the computed outputs (money, bps, spread, fees, saving), the confidence labelling scheme and the prerequisite, which is enough to call it correctly. It does not describe the response envelope or what happens when no eligible route exists, a minor gap given no output schema.

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%, including the complex existing_provider object, so the schema already carries parameter meaning. The description only reinforces that existing_provider is mandatory and implies the analysis_id read path, both of which are visible in the schema. Baseline 3 is correct.

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?

Opens with a specific outcome: 'Where the money leaks on your current provider: total cost against the official rate in money and bps, split into FX spread and fees'. That is a concrete computation, not a restatement of the name. It never names which sibling it replaces (e.g. calculate_payment_cost or compare_payment_providers), so an agent comparing tools in the payment-intelligence cluster gets no explicit disambiguation.

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?

'Needs existing_provider' states a hard prerequisite, and 'Free: shares the route-assessment allowance' flags quota interaction with the route-assessment tools. 'One analysis (POST /api/v1/payment-analyses), the same service for every payment-intelligence tool' clarifies the endpoint model. There is no explicit when-not-to-use or pointer to an alternative tool, which keeps it below a 5.

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