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

Beyond readOnlyHint/destructiveHint, the description adds meaningful context: results come back newest first, nothing is marked as read (a real IMAP concern), and search runs through local Proton Mail Bridge requiring a Bridge-inclusive plan with Bridge running. That prerequisite disclosure is valuable and not in annotations. It omits anything about result ordering nuances or paging behavior, but the essentials are covered.

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 front-loaded with the action and scope and is short. However, the Bridge prerequisite is stated twice: once as 'run by Proton Mail Bridge on this computer' and again in the final sentence. Removing the redundant sentence would tighten it without losing 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 read-only search tool with an output schema and fully described parameters, the description covers scope, ordering, side effects, and prerequisites. Pagination is left to the schema, which is appropriate. The only gap is the lack of explicit sibling routing.

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 baseline is 3. The description adds only marginal value: folder defaults to INBOX and the special 'All Mail' value searches every message, which is not in the schema. It says since/until 'narrow it to a period of days' but adds no format detail beyond what the schema already states.

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 first sentence gives a specific verb, resource, and scope: searching one folder of a Proton Mail account, matching headers and text, newest first. It implies, but does not explicitly name, why one would pick this over proton_list_emails. The scope constraint (only one folder) is a meaningful distinction that only shows up indirectly.

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 explains the folder-scoping rule and mentions 'All Mail' as a way to search everything, which hints at use. However, it never directly contrasts this with proton_list_emails or proton_read_email, so when to use this versus those siblings is left to inference.

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