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

Annotations already flag this as a non-read-only, destructive, idempotent, closed-world write, and the description adds substantial context beyond them: replacement with no history, the inability to blank the reply, refusal of links and flagged words, dual visibility surfaces (creator page after approval vs. supporter receipt link), and that no notification is sent. This is exactly the mutation detail an agent needs.

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 verb, resource, and the length constraint, then layered with visibility and side-effect clauses. Every sentence carries distinct behavioral information, though the visibility sentences are dense and could be tightened; there is no filler or restatement of the title.

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?

An output schema exists, so return values need no explanation, and the description covers the remaining gaps: scope (one supporter), validation limits, replacement semantics, visibility timing, and the absence of notification or approval side effects. Nothing required to invoke it correctly 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 coverage is 50%: 'reply' is documented in-schema but 'id' is not. The description compensates by tying the write to 'one supporter' (implying id targets a single supporter) and by disclosing validation rules for reply — 280-character cap, links and flagged words refused — that the schema's maxLength alone does not convey.

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 and resource ('Write or replace the thank-you beside one supporter') plus a hard constraint (280 characters). It further differentiates itself from nearby write-siblings by declaring 'Does not approve anyone and sends nothing', so an agent can separate it from approve_support 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 on when this applies (a thank-you for one supporter) and explicit exclusions relative to siblings ('Does not approve anyone and sends nothing'), which rules out approve_support. It stops short of naming a preferred alternative tool or stating prerequisites for the supporter's state, so it is clear but not fully routing.

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