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

Annotations already cover readOnlyHint=false and idempotentHint=true, and the description adds meaningful context beyond that: it specifies exactly what the preference controls (Hostlo emails/pages) and explicitly excludes the assistant's reply language. This surfaces an important side-effect distinction that the annotations do not convey.

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?

Three sentences with no filler: purpose/scoping first, then allowed values, then a key usage clarification. Each sentence earns its place and the structure front-loads what the tool does before diving into nuances.

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 one-param tool with no output schema, the description covers purpose, scoping, and a behavioral distinction that could affect the agent's response. It does not explicitly state what the tool returns (e.g., current preferences after read/change), but given the tool's simplicity and the schema's completeness, this is a minor gap rather than a critical omission.

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 schema already documents the 'language' parameter, allowed values (en/km), and the null/omit behavior. The description repeats those values and adds no new parameter-level syntax or edge cases; its extra language about replies is behavioral rather than parameter semantics. Baseline of 3 is appropriate.

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-resource pair: 'Read or change the person's Hostlo preferences', then immediately narrows the current scope to language ('English (en) or Khmer (km)'). This fully distinguishes the tool from siblings, none of which manage preferences, and the annotation title reinforces the language focus.

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 an explicit trigger: 'Use it when they ask to read Hostlo in Khmer or English.' It also proactively clarifies a potential misapplication by noting 'Your own replies stay in whatever language you are speaking with them,' which prevents the agent from using this tool to change its own output language.

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