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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so safety is covered. The description still adds real behavior beyond that: 'posts nothing' confirms the local, non-mutating scope, and the live-midpoint valuation with a 0 fallback on lookup failure is a genuine operational detail. It stops short of describing output shape, but the output schema covers that.

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 deliverable, then behavior, then routing alternatives — a sensible order and no filler. The 'Reads the local account' fragment is mildly redundant with readOnlyHint, which is the only slack in an otherwise tight definition.

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?

An output schema exists, so return formatting need not be explained, and the schema fully documents both parameters. The description supplies purpose, mutation behavior, valuation semantics and sibling routing — everything an agent needs to select and call it.

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 both 'format' (with its enum-like choices) and 'account' are fully documented in the schema, and the description adds no param-level meaning. A baseline 3 is appropriate when the schema does the heavy lifting.

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 ('Render one account's ROI, Sharpe, win rate and P&L as a postable text card') and immediately names the scope ('one account'). It is clearly distinguishable from stats, pk_card and share_content, which are named explicitly.

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 final sentence routes the agent explicitly: 'Use stats for raw numbers, share_content for platform and template choices, or pk_card to compare two accounts.' This tells the agent which sibling to pick and under what condition, leaving nothing to inference.

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