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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=true, but the description adds real value beyond them: immediate customer visibility ('sees it right away'), the confirmation requirement and its override, and the API-key/access prerequisite. These are behavioral facts an agent would not learn from the annotations.

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 core action, then attachments, then behavior and auth requirements. Efficient overall, though the confirmation guidance is split across two sentences with mild redundancy ('By default you confirm each call' vs 'confirm with the user before each call').

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 3-parameter mutation tool with no output schema, the description covers the key unknowns: scope (existing conversation), attachment mechanism, delivery timing, confirmation policy, and auth. Nothing critical to correct invocation 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 body, lead_id and attachment_urls. The description's note about 'optional photos or files by URL' adds only marginal gloss over the attachment_urls schema entry, so the 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 (send) and resource (message) plus the scope: an existing conversation with a customer. This implicitly separates it from thumbtack_reach_out_to_opportunity, which establishes new contact. However, it never explicitly names siblings like thumbtack_reply_to_lead or thumbtack_send_estimate, so differentiation relies on 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?

The phrase 'existing conversation' gives implied usage, and the confirmation instructions describe a procedural precondition. But it offers no explicit when-to-use/when-not guidance against the sibling message tools (reply_to_lead, reply_to_review), leaving the agent to infer selection.

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