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

Annotations already declare destructiveHint=true, readOnlyHint=false, and idempotentHint=false, so the safety profile is covered. The description adds genuinely non-structured context: the writability precondition and the fact that only a partial confirmation (uuid, title, modified state) comes back rather than the whole Riddle. It does not say what happens on a gate failure or whether the prior title is recoverable, which keeps it below a 5.

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?

Three short sentences: operation, return scope, precondition -- front-loaded and free of filler. The final sentence is telegraphically compressed ("Only if ... : riddle://reference/concepts/access"), which costs a little readability but wastes no words.

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 with full annotations and no output schema, the definition covers what it does, what comes back, and the permission gate. Only the failure mode when writableByThisKey is false is left unstated, a minor gap rather than a blocking one.

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 both parameters are fully documented in the structured schema. The description restates UUID and the new title but adds no format, constraint, or uniqueness semantics beyond what the schema already provides, 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?

"Renames a Riddle with the specified UUID" states a specific verb and resource, and the second sentence bounds the result to a confirmation payload. An agent can distinguish this from riddle_builder_update, riddle_move, or question_bank_rename without opening another 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 an explicit precondition for invocation -- origin.writableByThisKey must be true -- and names riddle_get / riddle_list as the way to check, plus a reference URI for access concepts. It lacks a stated when-not or alternative path for the case where the gate fails, but the eligibility condition itself is clear.

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