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

Annotations already declare readOnlyHint=false and destructiveHint=false. The description adds real value beyond them: it discloses the return shape (only uuid, title, modified state, not the full Riddle) and an authorization precondition on origin.writableByThisKey. Minor gap: idempotentHint=false is asserted without explanation, though renaming to the same title is arguably repeatable.

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 clauses, front-loaded with the action and the return-value clarification before the conditional access note. No filler. The trailing reference path is terse to the point of being slightly cryptic but does not bloat the text.

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?

With no output schema, the description usefully explains what is returned, and it covers the key authorization gate. For a two-parameter mutation this is nearly complete; only failure behavior and the sibling-overlap question remain unaddressed.

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 UUID and title are already documented in the schema. The description restates the UUID/title intent but adds no format, constraint, or validation detail beyond what the schema provides. 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?

States a specific verb+resource: 'Renames a Riddle with the specified UUID.' This is clearly distinct from siblings like riddle_delete, riddle_move, and riddle_get. It does not explicitly contrast with riddle_builder_update, which could plausibly also alter a title, so sibling differentiation is only partial.

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?

Provides an explicit precondition for use: only when origin.writableByThisKey is true, with pointers to riddle_get and riddle_list for checking that, plus a reference doc. It does not state when to prefer this over riddle_builder_update or note what happens on failure, but the usage context is clearly defined.

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