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

Annotations already indicate this is a write operation (readOnlyHint=false) and not idempotent. The description adds that a lost reason is required, which is a useful behavioral constraint, but it doesn't disclose side effects (e.g., whether the deal becomes immutable, affects reporting, or is reversible). This is acceptable given annotations, but not rich.

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 two short, direct sentences. It front-loads the primary purpose and immediately notes the key prerequisite. There is no fluff or redundant information.

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 simple state-change tool, the description covers the core action and the mandatory input. With an output schema present and full parameter descriptions, the description is adequate. However, it lacks context about postconditions (e.g., whether the deal is closed, audit trails, or restrictions) which would be valuable for an AI agent deciding on this tool.

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?

The input schema already provides full descriptions for both parameters (dealId: 'The deal ID', reason: 'Why the deal was lost'), with 100% coverage. The description's mention of 'requires a lost reason' merely reinforces a required parameter without adding new semantic detail, so it meets the baseline but doesn't exceed it.

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 action: 'Mark a CRM deal as lost.' This specifies the verb (mark), the resource (CRM deal), and the desired state (lost), distinguishing it from sibling tools like mark_deal_won or update_deal_stage. The requirement for a lost reason further clarifies the intent.

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 implicitly communicates when to use this tool: when a deal is decided to be lost and you need to record that outcome. However, it does not provide explicit exclusions or mention alternative tools (e.g., 'instead of updating the stage manually'), so it falls short of a full 5.

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