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

Annotations provide only destructiveHint=true, so the description carries most of the burden and delivers: it flags that this MUTATES Text-Em-All data, SPENDS CREDITS, and sends immediately (i.e., irreversible once sent). It also names the return value. Missing are auth/permission requirements and any rate-limit or delivery-failure behavior.

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 warning about mutation and credit spend is front-loaded, followed by what it does, the endpoint, the prerequisite, and the return value, in a dense few sentences. Every clause earns its place with no padding.

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 7-parameter mutation with a nested 'fields' object and no output schema, the description covers the essentials: write semantics, cost, prerequisite, and that it returns the conversation. It leaves credential/permission prerequisites and schema-override behavior of 'fields' unaddressed, but nothing blocking is missing.

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 all seven parameters, including the note that textNumberId comes from list_text_numbers. The description restates the textNumberId source but adds no format, range, or merge-behavior detail beyond the schema's own 'fields' documentation. 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 (sends), resource (1:1 conversation text message), and scope (single contact, from one of your toll-free numbers), plus the underlying endpoint POST /v1/conversations. The '1:1 ... single contact' framing cleanly separates it from sibling create_broadcast, so an agent can route without opening a 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?

Gives clear context for use ('immediately', '1:1', 'single contact') and explicitly routes to a prerequisite sibling: textNumberId comes from list_text_numbers. It stops short of stating when NOT to use it (i.e., use create_broadcast for bulk sends), which keeps it from a 5.

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