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

readOnlyHint=true already establishes the safety profile, so the description's job is incremental. It adds the exclusivity constraint on the filter set, but says nothing about default page size, pagination behavior beyond what 'until' implies, or what a response contains. Useful but partial against a lowered bar.

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 resource, then the critical constraint, then a short note. Three compact clauses with no padding, though the bare 'Missive: GET /conversations' adds little for an agent that already has the tool.

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 15-parameter, no-output-schema read tool, the description covers the one non-obvious failure mode (filter exclusivity) while the schema carries defaults and per-parameter meaning and annotations carry the safety profile. Return shape is unspecified but that is a minor omission for a list endpoint.

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 every parameter, making 3 the baseline. The description does add one genuinely schema-absent rule — that exactly one mailbox-type filter must be supplied — which raises the value, but it leaves limit, until, and the two contact/organization filters unaddressed.

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 ('List conversations (email/chat threads)') and extends scope with the HTTP endpoint. It is clearly separable from read-oriented siblings like missive_get_conversation and message-level tools, though it does not explicitly name any alternative.

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 a strong invocation rule — EXACTLY ONE mailbox-type filter out of an enumerated set — which is exactly the kind of guidance an agent needs to avoid invalid calls. It stops short of saying when to prefer this over siblings such as missive_list_conversation_messages or missive_get_conversation.

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