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

Adds value beyond the annotations by disclosing the non-waiting behavior and the return shape ("summarised by when it came, its sender and the kind of its code or link, never its content"). However, annotations declare readOnlyHint=false on what reads as a pure count; the description never explains the write side effect (that results are added to the run report, only hinted at in the run_id parameter). That gap keeps it at 3.

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, front-loaded with the verb and resource, then the sequencing rule, then the return summary. Nothing is redundant with the title or restates the schema.

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 8 parameters and no output schema, the description usefully covers what comes back (time, sender, kind of code/link, not content) and when to call it. It does not mention result limits, ordering, or how the count relates to run-report output, which are minor given full schema coverage.

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 every parameter including the enum values and subtype list is already documented in structured data. The description only gestures at filters via "when it came, its sender and the kind of its code or link", adding little beyond the schema. Baseline 3 applies.

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 ("Counts the emails that reached the address") plus a concrete use case ("exactly one verification email"). The line "Doesn't wait" implicitly contrasts it with the wait_for_code/wait_for_link siblings, but the closest read sibling, check_email, is never named, so the agent must infer the split.

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?

Gives explicit sequencing guidance: "call it after the wait for the first email has returned, so a duplicate has had time to arrive." That is a real when-to-use rule an agent could otherwise get wrong. It stops short of naming alternatives such as check_email or expect_no_email, so there are no explicit exclusions.

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