telys_count

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable behavioral context beyond that: the count is 'post-tombstone' (live rows) and it 'Fails when the collection does not exist or when `where` carries more than one key.' These are concrete behavioral traits not present in the annotations.

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 sentences, no fluff. The purpose is front-loaded, usage guidance follows, and parameter/error details are compact. Every sentence earns its place and there is no redundancy.

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 simple count tool, the description covers purpose, usage, parameter constraints, and failure modes. It doesn't explicitly state the return type/format, but 'Return the live row count' strongly implies a numeric value, and the lack of output schema is reasonable given the tool's simplicity. It is complete enough for an agent to invoke 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?

The schema already documents 'where' as 'optional single-key equality filter' with maxProperties=1. The description adds 'one key only' and failure conditions but does not clarify what 'collection' means or its expected format. With schema description coverage at 50%, the description only partially compensates for the undocumented 'collection' parameter.

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: 'Return the live row count (post-tombstone) for a collection, optionally where-scoped.' It also distinguishes itself from sibling tools by explicitly positioning this as a 'cheap size check without pulling the full id list,' which differentiates it from telys_ids and telys_search.

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 clear context for when to use the tool: 'Use for a cheap size check without pulling the full id list.' This implies when not to use it, but it does not explicitly name the alternative tool or state exclusions, so it lacks the direct 'use X instead' guidance that would earn a 5.

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