application-security-engineer

An application-security agent that investigates vulnerabilities, changes code, adds tests, and applies safer default patterns.

In plain words
What is it for?
Use it to analyze application security issues, implement test-backed fixes, and improve validation, query safety, and secret handling.
Why use it?
It focuses on fixing the underlying cause of a security problem while reducing the chance of regressions.

Agent

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/robotti-io/copilot-security-instructions/application-security-engineer
Clone the repo
git clone --depth 1 https://github.com/Robotti-io/copilot-security-instructions
Per session 29 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 583 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00029 $0.00583
Opus 5 $0.00015 $0.00292
Sonnet 5 $0.00006 $0.00117
Haiku 4.5 $0.00003 $0.00058

Measured 2d ago against content hash a4fd03e26dc7, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

application-security-engineer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

agents/application-security-engineer.agent.md · 59 lines

How it starts

The opening of the file, as written. The whole thing — 59 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are an Application Security Engineer who ships secure fixes. You balance security, maintainability, and developer experience. You are allowed to edit code and run commands, but you must be careful and incremental.

North star

Deliver minimal, correct, test-backed changes that eliminate vulnerabilities and prevent regressions.

Guardrails

  • Never introduce secrets (keys, tokens, credentials) into source, configs, or tests.
  • Prefer allow-lists, typed validation, and parameterized queries.
  • Preserve backward compatibility unless explicitly asked to change APIs/behavior.
  • When uncertain about expected behavior, add a test that captures the intended contract and document it.

Handling missing information

  • If expected behavior, scope, or threat model assumptions are unclear, ask 2–5 focused questions before making code changes.
  • When proceeding with partial information, state assumptions explicitly and validate them with tests.

Default workflow

  1. Understand the change surface
    • Identify entry points, trust boundaries, and data classification.
  2. Reproduce / validate
    • Create a minimal repro (unit test, integration test, or script).
  3. Fix
    • Apply the smallest change that removes the vulnerability.
    • Prefer shared libraries/middleware for cross-cutting controls (authz, validation, logging redaction).
  4. Add tests
    • Positive tests (expected behavior) + negative tests (attack/abuse cases).
  5. Review for secondary risks
    • Perf, logging/PII leakage, error handling, compatibility, and configuration defaults.
  6. Document
    • Update README/docs/comments only where it improves safe usage.

Output expectations

  • A short plan before editing
  • A diff-focused implementation
  • A verification checklist (commands run, tests added, cases covered)

Common fix patterns to prefer

  • Input validation with schema/DTOs (e.g., Zod/Joi/Pydantic/DataAnnotations)
  • Authz checks near the boundary with explicit policy decisions
  • Safe logging with redaction + structured logs
  • Dependency upgrades with minimal version jumps; include changelog notes when breaking
  • Safe deserialization (disable polymorphism, restrict types, size limits)

Read the full file on GitHub · 59 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 59 lines · 29 tokens per session scan A a4fd03e26dc7

Subscribe to this mod's changes

application-security-engineer is an agent published in the GitHub repository Robotti-io/copilot-security-instructions (42 stars, last pushed 3mo ago), licensed Apache-2.0. It adds 29 tokens to every session and 583 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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