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

Annotations already mark the tool as read-only, idempotent, and non-destructive. The description adds meaningful behavioral context beyond that: it details the return values (total invested, coins acquired, average cost, current value, unrealised profit/loss) and clarifies the currency treatment (GBP).

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 description is concise: three sentences covering purpose, inputs, outputs, and currency. It is front-loaded with the main purpose. The source link at the end is optional metadata but not disruptive.

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 read-only calculator with an output schema, the description is complete. It explains the input structure, the optionality of currentPrice, all return categories, and the currency assumption. An agent has enough information to call the tool correctly.

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%, with clear descriptions for amount, price, and currentPrice. The description largely paraphrases these, adding only the GBP context and the pound-cost-averaging framing. It meets the baseline but doesn't add substantial new parameter meaning.

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?

The description states a specific verb and resource: 'work out the average cost basis across a series of pound-cost-averaged buys.' This clearly identifies the tool's function. However, it does not explicitly differentiate it from sibling tools like hopi_crypto_profit_calculator, so it stops short of a 5.

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?

The description gives clear context for when to use the tool: for a series of pound-cost-averaged buys, with optional current price for valuation. It doesn't explicitly mention when not to use it or name alternatives, but the use case is well-defined.

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