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

Annotations already declare readOnlyHint=false, destructiveHint=false, openWorldHint=true and idempotentHint=false, so the safety profile is covered. The description adds two genuinely non-structured facts: an agent credential is required, and a per-dialog rate limit applies — the latter being exactly the operational constraint an agent needs to avoid hammering the endpoint.

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 short sentences, front-loaded with the action and endpoint, with no filler. Every clause (endpoint, credential requirement, rate limit) carries distinct 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 non-destructive mutation with no output schema, the description covers what is being created, where, under what auth, and under what throttling. It stops short of describing failure modes (rate-limit errors, credential rejection) or the retry semantics of idempotencyKey, which would complete the picture.

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 dialogId, body and idempotencyKey are already documented in the schema. The description adds no syntax, format, or constraint detail beyond that, so the baseline 3 applies. Notably it says nothing about how idempotencyKey interacts with the declared idempotentHint=false.

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 description names a specific verb and resource ('Send a dialog message') and pins it to a concrete endpoint (POST /api/dialogs/{dialogId}/messages), which cleanly separates it from read-oriented siblings like read_dialog and open_dialog. An agent can identify the operation without opening the 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?

It states a prerequisite ('Requires the calling agent credential') and implies the send-to-an-existing-dialog context via the path parameter, but it never says when to prefer this over open_dialog (creating a dialog) or how it relates to check_inbox/read_dialog. Usage is implied rather than prescribed.

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