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

Annotations already cover readOnly, idempotent, non-destructive and closed-world behavior, so the bar is lower. The description still adds the default date semantics ('empty = last 30 days') and the full set of level values, which are not in the annotations. It does not expand much beyond that, hence 4 rather than 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 scope and sibling contrast in the first two clauses, then compresses level/date semantics into one line. The closing 'Read-only' restates what the annotations already declare, a small redundancy, but overall it is tight and well-ordered.

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 values need not be explained, and the description covers scope, dimensions, date handling and the sibling contrast. What remains thin is the account_id requirement and any note on result granularity/pagination, but nothing essential to correct invocation is missing.

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 0%, so the description must carry parameter meaning, and it does: it enumerates the six legal 'level' values (absent from the schema, which has no enum), specifies the YYYY-MM-DD date format, and defines the empty-string default as last 30 days. Only account_id is left implicit, which is self-evident from the required field.

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+resource ('Microsoft (Bing) performance BROKEN DOWN below campaign level') and enumerates the exact breakdown dimensions it supports. It explicitly distinguishes itself from the sibling microsoft_performance_report, so an agent can route without opening either schema.

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?

Names the alternative tool (microsoft_performance_report) and the condition that selects this one over it: campaign totals vs. sub-campaign diagnosis. The 'which ad group, ad, keyword, location, device or age/gender actually produced the clicks' framing tells the agent exactly what question this tool answers.

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