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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds genuine behavioral context beyond that — result ordering ('newest first'), the exact result shape, and the not-connected error path. It stops short of covering pagination or rate limiting, so a 4 rather than a 5.

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-loads the core action, then the query syntax, then the sibling routing rule, then the error fallback. Every sentence carries a distinct actionable fact with no repetition of the schema or title.

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?

With no output schema, the description compensates by enumerating the returned fields; with only a readOnlyHint annotation, it adds ordering and error-handling detail. An agent has everything needed to call this correctly without opening anything else.

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 coverage is 100%, so baseline is 3, but the description adds real value the schema does not: it explains that `query` is Outlook KQL and demonstrates the syntax (from:, to:, subject:, hasattachments:, received>=), which meaningfully improves query construction.

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 ('Search the user's connected Outlook mailboxes and return matching messages') and enumerates the returned fields, giving the agent a precise picture of the operation. It explicitly distinguishes itself from the Gmail siblings ('Use this, not the Gmail tools, for Outlook mailboxes').

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?

Explicitly names the alternative (Gmail tools) and the condition that selects this one (Outlook mailboxes), plus a concrete sub-case: pass folder='sentitems' for sent mail. It also tells the agent what to do on failure — surface the returned connection link to the user.

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