add_custom_header_to_request

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

The description explains the core behavior (adding a header before sending) but fails to address the navigateUrl and clickSelector parameters in the schema, which reference actions not mentioned in the description. With no annotations, this omission leaves behavior ambiguous for those parameters. It also doesn't clarify matching semantics (e.g., glob vs regex) or side effects.

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?

The description is exactly two sentences, with the core action front-loaded in the first sentence and the sibling comparison in the second. No extraneous words, and the structure is ideal for quick scanning.

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?

Despite its concise core, the tool has six parameters and no output schema or annotations. The description fails to reconcile the presence of navigateUrl and clickSelector, which appear to belong to a different action model, leaving an agent uncertain about when those parameters are relevant. This incompleteness is significant for a mutation tool.

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 input schema provides descriptions for all six parameters (100% coverage), so the baseline is 3. The description adds only a high-level reference to 'flat parameters' and does not elaborate on individual parameter usage beyond what the schema already states.

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 and resource ('Add a custom header to matching requests before sending') and explicitly distinguishes from a sibling tool ('Simpler alternative to intercept_and_modify_traffic'). This makes the tool's purpose unambiguous and clearly differentiates it from the most related sibling.

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 provides clear context by positioning this tool as a 'simpler alternative' to intercept_and_modify_traffic, implying it should be used for straightforward header additions. However, it does not explicitly state when not to use it or provide alternative conditions beyond that single comparison.

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