webmcp_list_tools

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

No annotations are provided, so the description carries the full burden. It explicitly states 'Side effects: none (read-only state access)' and lists prerequisites, which addresses safety and failure conditions. It doesn't cover error responses or rate limits, but for a read-only listing operation this is sufficient.

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 well-structured with separate sentences for action, side effects, prerequisites, return value, and usage. It is front-loaded with the main purpose and contains no filler. Every sentence earns its place.

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?

The description includes the core purpose, side effects, prerequisites, and return type. It doesn't specify exact error behavior when prerequisites aren't met, but for a listing tool this is acceptable. The lack of an output schema is partially compensated by stating 'JSON array of available tools with schemas and frame IDs.'

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?

There is only one parameter (instance_id) and the schema description covers it 100% (optional, default instance). The tool description adds no additional semantic information about the parameter beyond what the schema provides, so the baseline score of 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?

The description states a specific verb and resource ('Lists all WebMCP tools') and clearly differentiates from siblings like webmcp_invoke_tool and webmcp_get_invocation by focusing on discovery. It also mentions the return type and purpose, making it unambiguous.

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 clear usage guidance: 'Use this to discover capabilities exposed by websites implementing WebMCP.' It implies when to use it (before invoking tools) but doesn't explicitly mention when not to use it or name alternatives. The purpose is distinct enough that this is adequate.

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