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

Beyond the annotations, the description discloses critical behavior: sends are never retried after 5xx/timeout, message_id reuse fails with ALREADY_EXISTS and can detect duplicate sends, and thread parameters are ignored in non-threaded spaces. This adds materially to the readOnly/idempotent/destructive hints.

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 dense but every clause earns its place, covering identity, scopes, formatting, threading, idempotency, return values, retry behavior, and exclusions. It front-loads the core action and distinguishes the tool from raw_request, making the length appropriate for the tool's complexity.

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 tool with no output schema and six parameters, the description is remarkably complete: it explains return fields, failure modes, duplicate detection, threading edge cases, and when to use an alternative tool. An agent has enough context to invoke it correctly and safely.

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?

Although schema description coverage is 100%, the description adds substantial meaning: markup syntax for text, thread_name sourced from thread.name, thread_key semantics, reply_option fallback vs or_fail, client- prefix rules for message_id, and space id formats. This goes well beyond the schema fields.

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 states a specific verb and resource: 'Sends a text message to a space AS THE AUTHENTICATED USER,' including identity and scope requirements. It also differentiates from sibling tools by explicitly carving out cardsV2 as app-auth-only and routing those to raw_request.

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 gives explicit when-to-use and when-not-to-use guidance: required scopes, membership prerequisite, thread fallback behavior, and the instruction to check with list_messages before re-sending after a 5xx/timeout. It even names raw_request as the alternative for app-auth card sends.

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