Messages API: Create a message

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

Annotations already declare the safety profile (write op, non-idempotent, non-destructive, open-world). Beyond that, the description usefully discloses that text is sent unchanged and that Persian/Arabic-Indic digits are accepted for IDs and numbers, plus the extra_body merge mechanism. It omits auth requirements and error behavior, which keeps it from a 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-loaded with the action, then the endpoint, then body fields, then the language/digit note. It is appropriately short and every sentence carries information; the Persian/Arabic-Indic note is slightly tangential but plausibly useful for this locale-focused API.

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 6-parameter mutation tool with no output schema, the description covers the call surface (endpoint, body fields, extra_body) but says nothing about what a successful create returns, error modes, or that echo_id comes back over websockets (only in the schema). Adequate but with clear gaps.

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 the schema already documents content, echo_id, extra_body and the three identifiers in detail; baseline is 3. The description restates the body fields (content, echo_id) and clarifies the extra_body escape hatch, but adds little beyond the schema's own descriptions.

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 ('Create a message') and even gives the full POST endpoint path with the resource hierarchy, so the agent knows exactly what it does. However, it never distinguishes this 'client' message creation from the sibling gapify_create_message, leaving the split between the two API surfaces to inference.

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?

There is no when-to-use guidance, no prerequisites (e.g. that a conversation must exist first), and no named alternative among the many message-related siblings (gapify_create_message, gapify_client_update_message). The endpoint path implies context but provides no explicit routing advice.

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