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

Annotations already carry the safety profile (readOnlyHint=true, openWorldHint=false, destructiveHint=false). The description adds genuinely useful operational disclosure beyond that: the story is fixed/deterministic, and 'Never invent, rewrite, summarise, or skip' warns the agent that the tool must return exact content and will not tolerate creative expansion or skipping. No contradiction with annotations; the read-only hint aligns with 'Return the requested next fragment.'

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 totaling roughly 22 words. Sentence one front-loads the core action and precondition; sentence two delivers the hard constraints. Every word carries weight and there is zero filler or repetition of schema content.

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?

This is a low-complexity tool: 2 parameters, 1 required, full schema descriptions, an enum on storyId, and safety annotations. The description covers what it does, when it applies, and its boundary constraints; the schema fully documents parameters; annotations document the safety profile. No material gap remains for an agent to invoke it correctly.

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 coverage is 100%, so the baseline is 3. The description adds meaning beyond the schema with the 'Never ... skip story fragments' clause: although the schema permits part values from 2 to 5, the description constrains usage to the immediate next fragment, preventing an agent from naively requesting part=5 after part=2. This operational constraint is genuine value-add over the schema text.

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 (Return) with a specific resource (next fragment of the fixed FICTURN story already open in the reader). The qualifier 'already open in the reader' and 'fixed' clearly distinguish it from the siblings browse_stories and start_story, and the prohibitions ('Never invent, rewrite, summarise, or skip') reinforce what the tool is not.

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 precondition 'already open in the reader' gives clear context for when this tool applies, implying start_story must have been called first, and 'fixed FICTURN story' separates it from browse_stories' discovery role. However, the siblings are never named explicitly, so the agent must infer the workflow rather than being told 'use X for Y'.

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