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

The description adds substantial behavioral context beyond annotations: payment via x402, input/output caps (16k chars input, 1k tokens output), text-only, no streaming. This complements and expands on the annotations (readOnlyHint=false, openWorldHint=true) without contradiction.

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 two sentences, front-loading core identity and then covering constrains efficiently. Every sentence earns its place with no fluff.

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?

Given the tool's complexity (4 params, output schema present), the description covers all essential aspects: API compatibility, payment model, caps, no streaming, and text-only limitation. With an output schema referencing standard Anthropic response shape, no further explanation is needed.

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?

With 100% schema coverage, the baseline is 3. The description adds value by clarifying that model is the only allowed value, system prompt counts toward input cap, messages are text-only, and max_tokens is clamped to 1024. This provides practical usage details beyond the schema.

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 clearly identifies the tool as an Anthropic-compatible /v1/messages endpoint for Claude Haiku 4.5, specifying the exact request/response shape and differentiating from siblings like post_v1_chat_completions by its unique API dialect and model.

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 provides explicit guidance on how to use the tool (point SDK at given base_url, pay per call) and notes important constraints (caps, no streaming). However, it does not directly contrast with alternative tools like post_v1_chat_completions, leaving some ambiguity about when to choose this over others.

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