Free keyword research tools: how to evaluate and choose

Short answer: A free keyword research tool is software that helps you discover search queries, estimate demand, and assess ranking difficulty without a paid subscription. The right choice depends on your workflow stage and each tool's query limits — verify both on the vendor's current feature page before building a process around any single option.

The right free keyword research tool for your workflow is the one that matches your current research stage, not the one with the most brand recognition. A tool that excels at seed discovery may offer nothing useful for competitor gap analysis; a tool with well-calibrated difficulty scores may hit its daily query cap before you finish a single content cluster. Evaluate on fit, not reputation.

Key entities you will encounter across this topic:

• Search volume: An estimate of how often a query is entered into a search engine per month
• Keyword difficulty (KD): A score (typically 0–100) indicating how hard it is to rank for a term organically — not standardized across tools
• Long-tail keywords: Phrases of three or more words, usually lower in volume but higher in specificity and intent clarity
• Seed keyword: A short, broad term used as a starting point for expanding a keyword list
• CPC (cost-per-click): The average bid advertisers pay for a keyword in paid search — a useful proxy for commercial intent
• Search intent: The underlying goal of a query — informational, navigational, commercial, or transactional
• Keyword gap analysis: Identifying terms a competitor ranks for that you do not
• SERP: The search engine results page, including organic results, ads, featured snippets, and People Also Ask boxes

The rest of this guide maps these concepts to a concrete evaluation framework and five-stage workflow so you can select and use free tools without building a process on assumptions you have not verified.

What a Free Keyword Research Tool Actually Does (and Doesn't Do)

Core Outputs: What Keyword Tools Measure

A keyword research tool takes a seed term or URL as input and returns a structured dataset. The core outputs across almost every tool in this category are the same: a list of related queries, an estimated monthly search volume for each, and some form of difficulty or competition score. Many tools also surface CPC data, SERP feature indicators (featured snippets, People Also Ask boxes, image packs), and related question formats.

These outputs are estimates, not measurements. No third-party tool has direct access to raw search engine query logs. What they surface is a model built from a combination of data sources — which is why the numbers differ from tool to tool and why the word "estimate" matters more than it might seem.

Why Free Plans Have Limits: The Data Cost Reality

Keyword data is expensive to acquire and maintain. Tools that surface volume estimates, difficulty scores, and SERP snapshots pay for crawl infrastructure, data licensing, or clickstream panel access to build their models. Free tiers exist to attract users into a conversion funnel, not to provide unlimited professional-grade access. As a result, free plans typically cap the number of queries you can run per day or month, limit the number of results returned per query, restrict export functionality, and exclude the freshest data updates.

This is the business model, not a flaw. Understanding it helps you plan around the limits rather than being surprised by them.

What Free Tools Typically Exclude (and How to Check)

Common exclusions on free tiers include: historical volume trend data beyond a short window, bulk keyword uploads, API access, competitor domain analysis, rank tracking, and full SERP snapshots. The specific exclusions vary by tool and change as vendors update their plans.

Before building a workflow around any free tool, check the vendor's current pricing or features page directly. Look for: the number of searches allowed per day or month, whether export is available (and in what format), how frequently the data updates, and whether a Google or email account login is required. Do not rely on third-party articles — including this one — for current plan specifics.

The Metrics That Matter: What to Look for in Any Keyword Tool

Search Volume: What the Number Means and What It Hides

Search volume is the metric most users look at first, and it is also the most misread. A monthly search volume figure is a model-based estimate of how many times a query was entered into a search engine over a rolling period — typically 12 months, averaged. It does not tell you how many of those searches resulted in a click, how many clicks went to organic results versus ads, or how the volume distributes across devices, geographies, or user segments.

Two practical implications: First, a volume estimate does not translate directly into available visitors — organic click-through rate depends on your ranking position, the presence of SERP features, and whether the query has a strong paid-search overlay. Second, volume figures are often bucketed, especially in tools that draw from Google's own data. Google Keyword Planner shows volume in ranges rather than exact figures for accounts with limited ad spend history. Treat volume as a directional signal, not a precise forecast.

Keyword Difficulty: How Tools Calculate It Differently

Keyword difficulty scores are not standardized. Each tool builds its own model, and the inputs vary: some weight the domain authority of pages currently ranking, others factor in the number of backlinks to the top-ranking URLs, and some incorporate on-page relevance signals. A score of 40 in one tool is not equivalent to a score of 40 in another.

What matters is internal consistency within a single tool. Use KD scores to rank keywords relative to each other within the same dataset, not to compare difficulty across tools. When evaluating a new tool, run a set of keywords you already understand — terms where you have ranking experience — and check whether the scores reflect your lived experience. That calibration step is more useful than trusting the absolute number.

Search Intent Signals: Informational, Commercial, Navigational, Transactional

Search intent is the purpose behind a query. The four standard categories are:

• Informational: The user wants to learn something ("how does X work")
• Navigational: The user wants to reach a specific site or page ("Notion login")
• Commercial: The user is researching before a purchase ("best project management tools for teams")
• Transactional: The user is ready to act ("buy X", "sign up for Y")

Some keyword tools label intent explicitly; others leave it to inference from SERP results. A reliable proxy: look at the top-ranking pages for a term. If they are all blog posts, the intent is likely informational. If they are product pages or comparison sites, it skews commercial or transactional. Matching your content type to intent is a more reliable ranking signal than volume alone.

Trend Data and Seasonality

A keyword's average monthly volume can mask sharp seasonal swings. Google Trends is the most accessible free source for visualizing how query interest moves over time — by week, month, or year — and for comparing relative interest between two terms in the same region. It does not surface absolute volume figures, but the relative index it provides is useful for identifying whether a keyword is growing, declining, or cyclical. Check trend data before committing editorial resources to a keyword that may peak once a year or is in structural decline.

Categories of Free Keyword Research Tools (and What Each Type Is Built For)

Google-Native Tools: Built-In Data, Built-In Constraints

Three tools from Google are relevant here, and each serves a distinct purpose.

Google Keyword Planner is designed for paid search campaign planning. It requires a Google Ads account (free to create, but the tool is optimized for advertisers). It surfaces keyword ideas, volume ranges, and competition levels for paid search. For organic SEO, the data is directionally useful — especially for identifying CPC as a commercial intent proxy — but the volume ranges can be broad, and the competition metric reflects paid auction competition, not organic ranking difficulty. Verify current access requirements and data display behavior on the Keyword Planner page directly, as Google adjusts these based on account activity.

**Google Search Console** shows you the queries your existing pages already rank for, along with impressions, clicks, and average position. It is not a discovery tool for new keywords — it only surfaces data for queries where your site has already appeared in results. It is, however, the most accurate source of performance data for your own content, because it draws from Google's own index rather than a model. Use it for Stage 5 monitoring (covered in the workflow section below).

Google Trends surfaces relative search interest over time, not absolute volume. Its strength is seasonality analysis and comparing the relative trajectory of two or more terms. It does not replace a volume-estimation tool but complements one.

Third-Party Freemium Tools: Richer UX, Tighter Daily Limits

Several established SEO platforms offer free tiers that include keyword discovery, volume estimates, difficulty scores, and SERP snapshots. These tools typically draw from a combination of clickstream data, web crawl data, and modeled estimates. The UX is generally more purpose-built for keyword research than Google's native tools, and they often surface long-tail keyword ideas, question-based queries, and related terms in a single view.

The trade-off is query limits. Free tiers in this category typically cap daily searches — the exact number varies by tool and changes as vendors update their plans, so check the current pricing or features page before relying on a specific limit. Export functionality is often restricted or unavailable on free tiers. These tools fit well for seed expansion and difficulty filtering in early-stage research when you are running a moderate number of queries per session.

Lightweight and No-Signup Tools: Fast but Narrow

A subset of tools requires no account creation and surfaces keyword suggestions quickly — often by scraping autocomplete data from search engines or aggregating question-based queries. Tools in this category are useful for rapid ideation and for surfacing the language real users use when searching.

Their limitations are significant: no volume data, no difficulty scores, no trend lines, and often no export. They work as ideation inputs, not as prioritization tools. Use them at the seed discovery stage, then pass the output through a tool that surfaces volume and difficulty before making content decisions.

YouTube Keyword Research: A Separate Data Layer

YouTube search operates on a different index from Google web search. A keyword that performs well in web search does not automatically have the same volume or competition profile on YouTube, and vice versa. Some third-party tools offer YouTube-specific keyword data on their free tiers; YouTube's own autocomplete is a zero-cost starting point. This category is covered in detail in its own section below.

How to Match a Free Keyword Tool to Your Workflow Stage

The most common mistake in keyword tool selection is choosing a tool based on brand recognition rather than workflow fit. The framework below maps five SEO workflow stages to the capabilities that matter at each stage — use it to identify which tool category to evaluate first, then verify current plan details on each vendor's page before committing.

Free Keyword Tool Selection Framework: Match Tool to Workflow Stage

Stage 1: Seed Keyword Discovery

Seed discovery does not require a sophisticated tool. The goal is to generate a broad set of root terms that reflect how your target audience describes their problem. Start with the language your customers use in support tickets, onboarding calls, and community forums — not the language your product team uses internally. Lightweight tools and autocomplete-based generators are well-suited here because speed and breadth matter more than precision. Verify on each tool's current page whether a signup is required and whether there are session limits.

Stage 2: Prioritization and Difficulty Filtering

Once you have a list of seed terms and expanded variants, you need volume estimates and difficulty scores to decide which terms to pursue. This is where third-party freemium tools or Google Keyword Planner become the primary resource. Run your candidate list through the tool, note volume ranges and difficulty scores, and filter for terms where the difficulty is within your current domain's realistic range. Check the vendor page for the current daily query cap before starting a large batch — hitting the limit mid-session means incomplete data.

Stage 3: Competitor Keyword Gap Analysis

Keyword gap analysis — identifying terms a competitor ranks for that you do not — is one of the most valuable research activities for a content strategy, and it is also one of the most commonly gated behind paid tiers. Before assuming a free tool covers this, check the vendor's current feature page explicitly. Some tools offer a limited number of competitor domain lookups per day on free plans; others restrict this entirely. If the free tier does not include gap analysis, the practical workaround is manual: search for your competitor's content, note the topics they cover, and run those topics through your volume and difficulty tool.

Stage 4: Content Planning and Clustering

Keyword clustering — grouping related terms under a single content piece or topic cluster — requires either export access (to work in a spreadsheet) or a tool with built-in clustering features. On free tiers, export is often restricted. If you cannot export, cluster manually within the tool's interface or copy results into a spreadsheet row by row. The decision criterion here is practical: estimate how many keywords you need to cluster per month and whether the free tier's export policy supports that volume.

Stage 5: Performance Monitoring with Existing Rankings

Google Search Console is the right tool for this stage, and it is free with no query cap on your own site's data. It shows which queries triggered impressions, how many clicks each received, and your average ranking position. Use it to identify which published pieces are gaining traction on terms adjacent to your target keyword — these are expansion opportunities. It does not show competitor data, and it only surfaces queries where your site has appeared, so it complements rather than replaces discovery tools.

Practical Limitations to Verify Before You Build a Process Around a Free Tool

Daily and Monthly Query Caps

Most free keyword tools enforce a cap on how many searches or lookups you can run within a given period. The cap may reset daily, weekly, or monthly depending on the tool. The specific limit is set by the vendor and changes over time — do not rely on a number you read in a third-party article. Before committing to a tool as part of your regular workflow, visit the vendor's current pricing or features page and confirm:

• How many searches are allowed per day and per month on the free tier
• Whether the cap applies to keyword lookups, domain lookups, or both
• What happens when you hit the cap (locked out until reset, or prompted to upgrade)

If the cap is lower than the number of queries your workflow requires in a typical session, the tool will create friction rather than remove it.

Export and API Access

Export functionality — downloading keyword lists as a CSV or spreadsheet — is a workflow multiplier. It lets you cluster keywords in a spreadsheet, share lists with collaborators, and feed data into a content calendar. On free tiers, export is frequently restricted: some tools allow a limited number of rows per export, others disable export entirely, and API access is almost universally a paid feature.

Before building a process that depends on exporting keyword data, check the vendor page for: whether CSV export is available on the free tier, how many rows are included per export, and whether API access exists (and at what plan level). If export is unavailable, factor in the manual effort of copying data into your own system.

Data Freshness and Update Frequency

Keyword volume estimates shift over time as search behavior changes — new terms emerge, seasonal patterns evolve, and some queries decline as products or topics fade. In most cases, this drift is gradual for evergreen topics, but it can be rapid for trend-driven or product-specific queries. Tools update their underlying data at different frequencies: some refresh monthly, others quarterly, and some on an irregular schedule. Stale data is not always obvious from the interface.

Check the vendor's documentation or help center for: how often the keyword database is updated, whether the volume figures reflect a 12-month average or a more recent window, and whether there is a "last updated" indicator in the tool's interface. For rapidly evolving topics, data freshness matters more than for stable, evergreen queries.

Account and Sign-Up Requirements

Some free tools require a Google account, an email signup, or a linked Google Ads account to access even basic features. This is worth knowing before you build a team workflow around a tool — if every team member needs a separate account and the tool limits lookups per account, the effective team-level cap is lower than the per-account cap suggests. Check: whether a signup is required, whether multiple users can share an account, and whether there are any domain verification steps (as with Google Search Console).

Are Free Keyword Research Tools Accurate Enough to Use?

Why Volume Numbers Differ Between Tools

Open the same keyword in three different free tools and you will likely see three different volume estimates. This is expected, not a sign that one tool is broken. The discrepancy exists because each tool builds its volume model from different inputs. Some use clickstream panel data — aggregated, anonymized browsing behavior from a panel of users — to infer search frequency. Others model from Google's own aggregated data, accessible through the Keyword Planner API or similar sources. Others use a combination of crawl data and proprietary modeling.

None of these approaches produces the exact figure that Google holds internally. They produce estimates, and the confidence interval around those estimates is wider than most tools communicate. The practical implication: treat volume as an order-of-magnitude signal.

Example (fictional): A keyword showing an estimated 500 searches/month versus one showing an estimated 5,000 searches/month represents a meaningful directional difference worth acting on. A discrepancy of roughly 1,200 versus 1,800 between two tools for the same keyword is more likely noise than a meaningful gap — use intent and competition signals to break that tie.

How to Cross-Reference Free Tools for Higher Confidence

The most reliable free-tool workflow involves running your candidate keywords through at least two independent sources and comparing directional agreement. If both tools agree that Term A has substantially higher volume than Term B, that agreement increases confidence in the relative ranking. If the tools disagree sharply on which term is larger, treat both as uncertain and look for additional signals — such as Google Trends relative interest or the number of competing pages in a SERP.

Google Trends is useful here as a tiebreaker: it does not give absolute volume, but it shows relative interest over time and can confirm whether one term is genuinely more searched than another in a given region.

When Accuracy Gaps Matter Most (and When They Don't)

Accuracy gaps matter most when you are making a binary decision between two similarly-sized keywords — choosing to write about Term A instead of Term B because it shows slightly higher volume. In that case, the volume difference may be within the margin of estimation error, and you should use intent, competition, and strategic fit as the deciding factors instead.

Accuracy gaps matter least when you are doing broad discovery — identifying which topic areas have any meaningful search demand versus which have none. At that level of resolution, even imprecise estimates are directionally reliable enough to guide content investment decisions. Build your process around the level of precision the decision actually requires.

Free Keyword Research Tools for YouTube: A Separate Evaluation

Why YouTube Keyword Data Differs from Web Search Data

YouTube is a search engine with its own index, its own ranking signals, and its own user behavior patterns. A query typed into YouTube reflects a different intent from the same words typed into Google: users on YouTube are looking for video content — tutorials, reviews, demonstrations, entertainment — and the autocomplete suggestions YouTube surfaces reflect what its own user base searches for, not what Google web searchers look for.

This means that web keyword tools, even well-regarded ones, do not transfer directly to YouTube research. A term with high web search volume may have low YouTube search activity, and vice versa. Tools built on web clickstream data or Google's web index do not capture YouTube query behavior unless they explicitly draw from YouTube's own data sources.

What to Look for in a YouTube-Specific Free Tool

When evaluating a free tool for YouTube keyword research, the relevant capabilities are: YouTube-specific volume estimates (not web search volume), tag and title suggestions based on YouTube autocomplete, and competitive analysis within YouTube results (how many videos target a given term, and what their view counts suggest about demand). Verify on each tool's current page whether the data source is YouTube-specific or a proxy from web search data — this distinction is not always clearly labeled.

Also check: whether the free tier includes YouTube data at all, how many lookups are allowed per day, and whether the tool surfaces trending terms within YouTube's own index.

Using YouTube Autocomplete as a Zero-Cost Starting Point

Before using any third-party tool, YouTube's own autocomplete is a free, real-time signal of what users are actively searching for on the platform. Type a seed term into the YouTube search bar and note the autocomplete suggestions — these reflect actual query patterns on YouTube, not modeled estimates. Extend this by appending letters of the alphabet after your seed term to surface additional variants. This approach has no query cap, requires no signup, and draws directly from YouTube's own data. Use it to generate a candidate list before validating with a tool that surfaces competitive data.

Building a Repeatable Keyword Research Workflow with Free Tools Only

Step 1: Generate Seed Keywords (No Tool Required)

Start before opening any tool. Write down every way your target audience might describe the problem your product or content solves. Pull language from your own support inbox, onboarding survey responses, and questions that come up repeatedly in user calls. Add the terms your competitors use in their page titles and H1s. The goal is a list of 10–20 root terms that reflect real user language, not internal product vocabulary.

Example (fictional scenario): A SaaS product that helps freelancers track client invoices might generate seed terms like "invoice tracker for freelancers," "client payment tracking," "freelance billing software," and "how to track unpaid invoices." These are not researched keywords yet — they are inputs for the next stage.

Step 2: Expand with a Free Discovery Tool

Take your seed list into a free discovery tool — a lightweight keyword generator or Google Keyword Planner — and expand each seed into a longer list of related terms, questions, and long-tail variants. The goal at this stage is breadth, not precision. Capture every variant the tool surfaces, including question-format queries ("how do I…", "what is the best…") and comparison queries ("X vs Y").

Keep the daily query cap in mind: if your seed list has 15 terms and the tool caps you at 10 lookups per day, split the expansion across two sessions. Verify the current cap on the vendor's page before starting.

Step 3: Filter by Difficulty and Intent

Run your expanded list through a freemium tool that surfaces keyword difficulty scores and intent signals. Filter out terms that are clearly out of reach for your current domain — high-difficulty terms dominated by large, established sites. Then filter by intent: separate informational terms (blog content candidates) from commercial and transactional terms (product page or landing page candidates). You should end the session with a shorter, prioritized list where each term has a plausible difficulty level and a clear content type implied by its intent.

Example (fictional scenario): From the invoice-tracker seed list above, "how to track unpaid invoices" might surface as informational with moderate difficulty — a blog post candidate. "Invoice tracker for freelancers" might surface as commercial with higher difficulty — a comparison or landing page candidate for a later stage.

Step 4: Confirm with a Second Free Source

Before assigning a keyword to your content calendar, cross-reference its volume estimate in a second free tool or in Google Trends. You are not looking for identical numbers — you are looking for directional agreement. If both sources indicate meaningful demand and Google Trends shows stable or growing interest, the keyword is a reasonable candidate. If the sources disagree sharply or Trends shows declining interest, flag the term for manual review before investing content resources.

Step 5: Cluster and Assign to Content Calendar

Group your validated keywords by topic and intent. Keywords that share a parent topic and the same intent type (informational, commercial) can often be addressed in a single piece of content targeting the primary term, with secondary terms covered naturally in subheadings and body copy. Assign each cluster to a content calendar slot, note the primary keyword, list the secondary terms, and record the intent type so the content brief reflects the right format (blog post, comparison page, tutorial, etc.).

Google Search Console closes the loop: once content is published and indexed, use it to monitor which queries are generating impressions and clicks, and feed that data back into the next research cycle.

Pre-Publish Checklist: Evaluating Any Free Keyword Tool Before You Commit

Use this checklist before building a repeatable workflow around a free keyword tool. Verify each item on the vendor's current pricing or features page — not from a third-party article.

Data and accuracy

• [ ] Does the tool specify its data source (clickstream, modeled, Google Keyword Planner API, or other)?
• [ ] Does it surface volume estimates or only relative interest?
• [ ] How frequently does the keyword database update — monthly, quarterly, or irregular?
• [ ] Does it show a "last updated" date or data freshness indicator?

Query and usage limits

• [ ] How many keyword lookups are allowed per day and per month on the free tier?
• [ ] Do limits apply to keyword searches, domain lookups, or both?
• [ ] What happens when you hit the cap — lockout until reset, or an upgrade prompt?

Export and workflow integration

• [ ] Is CSV or spreadsheet export available on the free tier?
• [ ] If yes, how many rows per export?
• [ ] Is API access available, and at what plan level?

Account and access requirements

• [ ] Does the tool require a Google account, email signup, or Google Ads account?
• [ ] Can multiple team members use the same account, or is it one account per user?
• [ ] Are there domain verification steps required?

Feature scope

• [ ] Does the free tier include keyword difficulty scores?
• [ ] Does it include intent labeling, or do you infer intent from SERP results?
• [ ] Does it include competitor domain analysis, or is that gated behind a paid tier?
• [ ] If you need YouTube data, does the free tier draw from YouTube's index specifically?

When a Free Tool Is Enough — and When to Consider Upgrading

Signs Free Tools Are Covering Your Needs

Free tools are genuinely sufficient for a range of common scenarios. If you are publishing fewer than a handful of pieces per week, running keyword research in focused sessions rather than continuously, and operating a site where the primary research need is discovery and basic prioritization — free tools can support that workflow without meaningful gaps. If Google Search Console is giving you enough performance data on published content, and a freemium tool is covering your discovery and difficulty-filtering needs within its daily cap, the workflow is functional.

Similarly, if your content strategy is topic-led rather than keyword-led — meaning you decide what to write based on audience problems and then confirm keyword demand — the precision of a paid tool adds less marginal value.

Workflow Signals That Suggest a Paid Tier Is Worth Evaluating

Specific friction points indicate that free tool limits are creating real costs. These include: hitting daily query caps before completing a research session, being unable to export keyword lists for clustering or sharing with collaborators, needing competitor domain analysis that is gated behind a paid tier, requiring fresher data than the free tier updates provide, or needing to run keyword research across multiple team members simultaneously (where per-account caps multiply the constraint).

If any of these friction points are slowing your publishing cadence or forcing manual workarounds that take more time than a paid subscription would cost, that is a workflow signal worth evaluating — but verify current pricing directly on each vendor's page before drawing that comparison.

Questions to Ask Before Paying for Any Keyword Tool

Before upgrading or purchasing a paid keyword tool subscription, work through these questions:

• Which specific free-tier limitation is creating the most friction in my current workflow?
• Does the paid tier of this tool directly remove that limitation, or does it add features I do not need?
• How many keywords do I realistically need to research per month, and does the paid tier's query allowance match that volume?
• Does my team need collaborative access, and how does the tool handle multi-user plans?
• Is there a trial period that lets me validate the paid-tier data quality before committing?

Verify current pricing and plan details directly on the vendor's pricing page — plan structures change, and any figure in a third-party article may be out of date.

FAQ

Is there a free AI tool for keyword research?

Several keyword research tools incorporate AI-assisted features — such as clustering suggestions, intent labeling, or content brief generation — on their free tiers. The specific tools offering AI features and the depth of those features on free plans change frequently. Check each vendor's current feature page to confirm what is included at no cost before building a workflow around it.

Are free keyword research tools accurate?

Free keyword tools produce estimates, not exact figures, because no third-party tool has direct access to raw search engine query logs. Volume numbers vary between tools due to different data sources (clickstream panels, modeled data, Google's aggregated data). They are accurate enough for directional decisions — identifying high-demand versus low-demand terms — but should not be treated as precise forecasts. Cross-referencing two independent sources improves confidence in relative rankings.

Is Google keyword research free?

Google Keyword Planner is accessible with a free Google Ads account, and Google Search Console is free for verified site owners. Google Trends requires no account. Keyword Planner is optimized for paid search and may show volume in broad ranges for accounts with limited ad activity. Verify current access requirements on each tool's official page, as Google adjusts these conditions periodically.

Is there a free keyword research tool for YouTube?

Some third-party SEO tools include YouTube-specific keyword data on their free tiers, though query limits apply. YouTube's own autocomplete is a zero-cost, no-signup starting point that reflects real query patterns on the platform. Check each vendor's current feature page to confirm whether their free tier draws from YouTube data specifically, or from web search data used as a proxy.

How many keywords should I research before writing a piece of content?

For a single blog post, researching one primary keyword and three to eight closely related secondary terms is a practical range for most workflows. The primary keyword defines the topic and intent; secondary terms inform subheadings and body coverage. For a content cluster or pillar page, the research scope is wider. The right number depends on topic complexity and how tightly related the secondary terms are — not on a fixed rule.