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Audit Context Building

Trail of BitsOfficialPublished by Trail of Bits

  • Skill
  • Research and analysis
  • Security
  • CC-BY-SA-4.0
  • Medium risk

From the author

Understand a codebase before looking for bugs in it - what each function assumes, what it guarantees, and what it depends on elsewhere. Use when starting an audit, threat model, or architecture review on unfamiliar code, and before any vulnerability-hunting pass.
— the description by Trail of Bits

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

Audit Context Building is a preparatory workflow designed to establish a comprehensive understanding of an unfamiliar codebase. By mapping out function-level assumptions, guarantees, and cross-function dependencies, it creates a structured dossier that serves as the foundation for subsequent vulnerability hunting. It explicitly separates the context-gathering phase from the bug-finding phase to ensure that security assessments are based on a complete, documented understanding of the system's logic rather than premature assumptions.

What it does

  • Analyzes function-level assumptions, guarantees, and dependencies.
  • Generates a central dossier and individual function records.
  • Identifies critical gaps where code relies on unverified assumptions.
  • Documents open questions and areas of ambiguity within the codebase.
  • Maps cross-function rules and reachability paths.
  • Provides a standardized format for auditing diverse targets like C, Solidity, or web services.

When to use it

  • At the start of a security audit, threat model, or architecture review.
  • When working with an unfamiliar codebase.
  • When previous audit attempts failed due to a lack of system-wide understanding.
  • Before performing any vulnerability-hunting or exploit-development tasks.

Advantages

  • Prevents premature or inaccurate vulnerability reporting.
  • Highlights 'nothing found' assumptions that are prime targets for security research.
  • Creates a shared, objective map of the system for the audit team.
  • Ensures that complex code paths are traced thoroughly rather than guessed.

Usage examples

“Run the audit context building workflow on the src/auth directory.”
The agent will analyze the functions in the specified directory, generating a dossier and individual function reports detailing assumptions and dependencies.
“Analyze the single function verify_signature in crypto.c using the context builder.”
The agent will perform a focused analysis of that specific function, returning a structured record of its internal logic and external requirements.

Install

  1. Download the skill as a ZIP:

    https://mp-staging.autogineer.com/agent-skills/trailofbits/audit-context-building/download
  2. Unzip it into the cross-client skills folder of your project:

    mkdir -p .agents/skills && unzip audit-context-building.zip -d .agents/skills

Documentation by Trail of Bits

Audit Context Building

Build understanding, not verdicts. This runs before anyone hunts for bugs, and feeds that work.

When to Use

At the start of an audit, a threat model, or an architecture review, when the code is unfamiliar. Also when an earlier pass produced findings nobody could judge, because no one had mapped out how the system fits together.

When NOT to Use

Do not name vulnerabilities, suggest fixes, write proofs-of-concept, or rate severity. Those belong to the hunting phase, which runs next and with the whole picture in hand. When the code counts on something and nothing checks it, record that plainly and move on — whether it matters is decided later.

Not worth the tokens on code you already understand.

Do not analyze in this context

The analysis is long, and this context needs to survive to use it. Dispatch it:

  • A codebase, or more than one function — run /audit-context-building:audit-context <path>. It orients, analyzes each function in its own subagent, and writes audit-context/DOSSIER.md plus one file per function under audit-context/functions/. Only compact records return here.

  • A single function — dispatch the audit-context-building:function-analyzer agent at it. It writes its prose to disk and returns a record.

Then work from what comes back: the index, the unenforced assumptions, the open questions. Read a function's file when you need its detail.

The workflow is what enforces this, not this text: a subagent bound to a return schema cannot return prose. Treat this section as routing, and route.

What comes back, and how to read it

Each record lists what must always be true (with the line that shows it), what the function takes on faith (with whatever establishes it), which functions it calls and what it needs from each, and anything still unclear. The dossier adds the rules that span several functions, who can reach what, and where the complicated parts cluster.

Two things matter more than the rest:

  • Assumptions marked nothing found. The code counts on something being true and nothing anywhere makes it true. This is the most useful thing to hand the hunting phase.

  • The open questions. An honest list of what is still unclear beats a confident answer that turns out to be wrong. Carry them forward instead of closing them out.

Where two records disagree, both are quoted rather than quietly reconciled. That is a fact about the code, not a flaw in the analysis.

The format

ANALYSIS_FORMAT.md defines it, and FUNCTION_MICRO_ANALYSIS_EXAMPLE.md works through examples in C and Solidity. Read them when extending this plugin or deciding whether a record can be trusted.

The format is the same whatever the target. What changes is what fills each slot, and what counts as a call you cannot see inside. DOMAIN_NOTES.md maps that across smart contracts, C and C++, decompiled firmware, and web services — read it when the target is not plain source code.

The rule that matters most: follow the calls. Whether a function is correct usually depends on something another function does, and you cannot see that from the caller alone. A limit looks enforced because the value came back from a function whose name suggests it was checked. So read the function being called, follow every path through it rather than only the one that succeeds, and say what makes each assumption true. When nothing does, use those words: nothing found. Every claim cites a line, or becomes an open question.

Files

Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Needs: Declares allowed tools

Security

What our scanner noticed· Medium risk

  • Zero-width Unicode characters

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

Attribution and licence

Published by
Trail of Bits
Publisher
Trail of Bits (Official)
Source
trailofbits/skills · plugins/audit-context-building/skills/audit-context-building · commit e4dd0bb
Licence
Creative Commons Attribution-ShareAlike 4.0 International (redistribution allowed)
  • LICENSE (added by AutoGineer from LICENSE)
  • ATTRIBUTION.md (written by AutoGineer)
Synced

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Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download audit-context-building.zip