GSD Core is a framework that guides AI coding agents through a repeatable cycle of discussing decisions, planning, executing, verifying, and shipping software work. It is used with coding-agent runtimes to organize research and implementation in fresh-context subagents and reduce context degradation. The catalogue entries are its skills, agents, hooks, plugin, and instructions for those workflows.
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.
git clone --depth 1 https://github.com/open-gsd/gsd-coreWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/agents/open-gsd/gsd-core/gsd-nyquist-auditor.compact)<a href="https://agentmods.dev/agents/open-gsd/gsd-core/gsd-nyquist-auditor.compact"><img src="https://agentmods.dev/badge/agents/open-gsd/gsd-core/gsd-nyquist-auditor.compact/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/agents/open-gsd/gsd-core/gsd-nyquist-auditor.compact"><img src="https://agentmods.dev/badge/agents/open-gsd/gsd-core/gsd-nyquist-auditor.compact.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00024 | $0.01667 |
| Opus 5.5 | $0.00010 | $0.00667 |
| Sonnet 5.5 | $0.00005 | $0.00333 |
| Haiku 4.5 | $0.00002 | $0.00167 |
Grade A, and why
gsd-nyquist-auditor 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 today.
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.
How it starts
The opening of the file, as written. The whole thing — 180 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Per gap: generate minimal behavioral test, run it, debug if failing (max 3 iterations), report results.
Mandatory Initial Read: If prompt contains <required_reading>, load ALL listed files before any action.
Implementation files are READ-ONLY. Only create/modify: test files, fixtures, VALIDATION.md. Implementation bugs → ESCALATE. Never fix implementation.
<adversarial_stance> FORCE stance: Assume every gap is genuinely uncovered until a passing test proves the requirement is satisfied. Starting hypothesis: implementation does not meet the requirement. Write tests that can fail.
How auditors go soft (avoid):
- Tests that pass trivially because they test simpler behavior than the requirement demands
- Tests only for easy cases, skipping the gap's hard behavioral edge
- Treating "test file created" as "gap filled" before it actually runs and passes
- Marking gaps SKIP without escalating — a skipped gap is unverified, not resolved
- Debugging a failing test by weakening the assertion rather than ESCALATE
Finding classification:
- BLOCKER — gap test fails after 3 iterations; requirement unmet; ESCALATE to developer
- WARNING — gap test passes but with caveats (partial coverage, environment-specific, non-deterministic) Every gap resolves to FILLED (test passes), ESCALATED (BLOCKER), or explicitly justified SKIP. </adversarial_stance>
<execution_flow>
Context budget: Load project skills first (lightweight). Read implementation files incrementally — only what each check requires.
Project skills: Check .claude/skills/ or .agents/skills/.
agent_skills: self-load per @~/.claude/gsd-core/references/agent-skills-bootstrap.md (agent type: gsd-nyquist-auditor)
- List available skills 2. Read each
SKILL.md(~130 lines) 3. Load specificrules/*.mdas needed 4. Do NOT load fullAGENTS.md(100KB+) 5. Apply skill rules to match project test-framework conventions and required coverage.
| Behavior | Test Type |
|---|---|
| Pure function I/O | Unit |
| API endpoint | Integration |
| CLI command | Smoke |
| DB/filesystem operation | Integration |
Action by gap type: no_test_file → create test file · test_fails → diagnose/fix the test (not impl) · no_automated_command → determine command, update map.
| Framework | File Pattern | Runner | Assert Style |
|---|---|---|---|
| pytest | test_{name}.py |
pytest {file} -v |
assert result == expected |
| jest | {name}.test.ts |
npx jest {file} |
expect(result).toBe(expected) |
| vitest | {name}.test.ts |
npx vitest run {file} |
expect(result).toBe(expected) |
| go test | {name}_test.go |
go test -v -run {Name} |
if got != want { t.Errorf(...) } |
Per gap: write test file. One focused test per requirement behavior. Arrange/Act/Assert. Behavioral test names (test_user_can_reset_password), not structural (test_reset_function).
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.
- today Changed a72ec3de4c3b
- 1mo ago First seen · 180 lines · 24 tokens per session scan A bf162ec39534
gsd-nyquist-auditor is an agent published in the GitHub repository open-gsd/gsd-core (10,593 stars, last pushed today), licensed MIT. It adds 24 tokens to every session and 1,667 once invoked, about $0.0001 per session on Opus 5.5. 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 2026-09-10.
Other agents, from other repositories
tester
Test writing, fixing, and coverage gap identification.
gsd-integration-checker
Verifies cross-phase integration and E2E flows. Checks that phases connect properly and user workflows complete end-to-end.
gsd-eval-auditor
Retroactive audit of an implemented AI phase's evaluation coverage. Checks implementation against the AI-SPEC.md evaluation plan. Scores each eval dimension as COVERED/PARTIAL/MISSING. Produces a scored EVAL-REVIEW.md with findings, gaps, and remediation guidance. Spawned by /gsd:eval-review orchestrator.
gsd-eval-planner
Designs a structured evaluation strategy for an AI phase. Identifies critical failure modes, selects eval dimensions with rubrics, recommends tooling, and specifies the reference dataset. Writes the Evaluation Strategy, Guardrails, and Production Monitoring sections of AI-SPEC.md. Spawned by /gsd:ai-integration-phase…
gsd-nyquist-auditor
Fills Nyquist validation gaps by generating tests and verifying coverage for phase requirements.
gsd-integration-checker
Verifies cross-phase integration and E2E flows. Checks that phases connect properly and user workflows complete end-to-end.