Set custom checker

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

Annotations already indicate this is a mutating, non-destructive, idempotent operation. The description adds meaningful behavioral context beyond annotations by explaining that the checker 'replacing exact output matching', which tells the agent what side effect to expect. No contradiction with annotations exists.

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?

Two sentences deliver the action, the behavioral change, and the usage condition with no filler. The key behavior ('replacing exact output matching') is front-loaded before the use-case guidance, making it easy for an agent to parse quickly.

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 two-parameter mutation tool with high schema coverage, annotations, and an output schema, the description is nearly complete: it states what the tool does and when to use it. It does not mention prerequisites such as an existing session or how the checker source should be formatted, but these are minor gaps given the output schema and parameter descriptions.

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 parameters session_id and checker_source are already documented in the schema. The description names the checker but does not add extra semantic detail like language, format, or constraints beyond what the schema provides, so baseline 3 is appropriate.

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 uses a specific verb ('Attach') and resource ('custom checker to a draft'), and it clearly distinguishes the tool's role by stating it replaces exact output matching, which sets it apart from sibling build tools like set_validator or set_solutions. The purpose is immediately understandable without needing the 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?

The description gives explicit when-to-use guidance: 'Use it when a problem accepts multiple correct answers or needs tolerance-based comparison.' It does not discuss when not to use it or name alternatives, but the usage condition is clear and actionable.

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