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

The description transparently details the output: 'Returns median + P90 + average cost from the org's last-30-day history' and 'Returns isUnknown=true with zero cost when no baseline exists yet.' This adds significant value beyond the annotations (readOnlyHint, idempotentHint) by explaining the specific data returned and edge cases.

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 and front-loaded: three sentences that state purpose, usage, and edge case. Every sentence adds value with no unnecessary words.

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?

Given the presence of an output schema (context signals indicate 'Has output schema: true'), the description adequately explains the return values and edge case. It covers all aspects needed for a pre-call estimation tool, and sibling tools are sufficiently differentiated.

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 baseline is 3. The description reinforces the tool's context (exact server/tool combo) but does not add new semantics beyond the schema descriptions. The parameters are clearly documented in the schema.

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 clearly states the tool's purpose: 'Estimate the USD cost of an MCP tool call BEFORE invoking it.' It specifies the exact verb (estimate), resource (USD cost), and timing, distinguishing it from sibling tools like 'get_today_cost' or 'list_top_tools' which serve different purposes.

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 provides explicit guidance: 'Use this to make spend-aware decisions in your agent — e.g. confirm with the user before invoking tools where the estimate exceeds your budget.' It also implies when not to use (when cost is irrelevant) and differentiates from siblings by focusing on per-call cost estimation.

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