bridge-agent

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fill_credential

Fills login forms using credentials stored in the OS keyring, keeping secrets out of observations. Use for password fields on web pages or native login dialogs.

Instructions

Fill a login form with a username and password that live in the operating-system keyring.

The secret is read by the executor and typed directly; it is never returned to you and never appears in the
observation. Use this instead of type_text for any password field. Works on web forms and on native login dialogs.
Returns a RESULT line naming the two fields that were filled, plus a fresh observation.

Input Schema

TableJSON Schema

Name	Required	Description
`ref`	No	Ref of the username or email field. Optional: when empty, the field labelled user, email, login or account is used.
`site`	Yes	Site key under which the user stored the credential with 'bridgeagent cred set <site>', e.g. 'company-portal'. Only keys allowed by the task or the permission manifest are accepted.
`submit`	No	Press Enter in the password field afterwards to submit the login form.
`password_ref`	No	Ref of the password field. Optional: when empty, the field labelled password is used.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Oct 16, 2026

TDQS

A4.3/5.0

Behavior5/5

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

With no annotations, the description carries the full burden and does so: it discloses that the secret is read by the executor, typed directly, never returned and never surfaced in the observation, and it describes the return shape (a RESULT line naming the two filled fields plus a fresh observation). That is exactly the security-relevant behavior an agent needs before touching a password field.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three tight sentences with no filler, and the secret-handling caveat and the type_text substitution are front-loaded where an agent will read them first. It is slightly longer than strictly required but each sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists and the description still summarizes the return, so return values are covered; secret handling, the alternative tool, and scope are all present. The only gap is failure behavior (missing keyring entry, disallowed site key), which is not addressed anywhere.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so ref, site, submit and password_ref are already fully documented in the schema, including defaults and the fallback labelling behavior. The description only says a username and password are filled, adding no syntax or constraint information beyond the schema, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (fill) and resource (login form) and an explicit source of truth (OS keyring credential), which no sibling does. It also names the sibling it replaces (type_text), so an agent can distinguish it without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives a clear routing rule: 'Use this instead of type_text for any password field,' plus the scope 'works on web forms and on native login dialogs.' It never states a when-not condition (e.g. what to do if the credential is absent from the keyring), so it stops short of full 5-level guidance.

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

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